Display device

ABSTRACT

To provide an active matrix display device in which power consumption of a signal line driver circuit can be suppressed, so that power consumption of the entire memory can be suppressed. A plurality of memory circuits which can write data of a video signal input to a pixel in one line period and can hold the data are provided in a signal line driver circuit of a display device. Then, the data held in each memory circuit is input to a pixel of a corresponding line as a video signal. By providing two or more memory circuits in a driver circuit, pieces of data of video signals corresponding to two or more line periods can be concurrently held in the memory circuits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active matrix display device in which input of a video signal to a pixel can be controlled by a driver circuit.

2. Description of the Related Art

In an active matrix display device, a switching element and a display element are provided in each of hundreds of thousand to millions of pixels arranged in matrix. Since application of voltage or supply of current to the display element is held to some extent by the switching element after a video signal is input to the pixel, the active matrix display device can be flexible on enlargement and high definition of a panel and has become the mainstream of future display devices.

There are a scan line driver circuit and a signal line driver circuit as typical examples of a driver circuit included in the display device. A plurality of pixels in one line or a plurality of lines are selected at one time by a scan line driver circuit. In addition, input of video signals to the pixels included in the selected line is controlled by a signal line driver circuit.

These scan line driver circuit and signal line driver circuit need driving at high frequency. In particular, while pixels of respective lines are selected by the scan line driver circuit, the signal line driver circuit needs to input video signals to all the pixels in the lines. Thus, driving frequency of the signal line driver circuit is extremely higher than that of the scan line driver circuit. For example, in the case of a VGA active matrix display device, driving frequency of a signal line driver circuit generally needs to be approximately 25 MHz. Further, in recent years, the number of pixels in one line of an active matrix display device has been increased because an image with higher definition, higher resolution and more gray-scales is displayed. Therefore, the signal line driver circuit needs driving at higher speed, and there has been a problem in that power consumption is high due to high driving frequency.

In view of the foregoing problem, Reference 1 (Japanese Patent No. 3338259) discloses a liquid crystal display device in which pieces of display data corresponding to adjacent two scan lines are compared with each other and transmission of the pieces of display data to the signal line driver circuit is not performed when the pieces of display data correspond to each other in order to suppress power consumption of a signal line driver circuit.

Further, Reference 2 (Japanese Patent No. 3593392) discloses a liquid crystal display device in which a wiring between a control IC and a signal line driver circuit is made shorter by providing the control IC so that output pins to the signal line driver circuit are close to the signal line driver circuit, so that power consumption due to wiring capacitance is suppressed.

SUMMARY OF THE INVENTION

It is naturally expected that lines where pieces of data correspond to each other exist discontinuously when an image is actually displayed. However, only comparison of pieces of data corresponding to adjacent lines can be performed by using the technique disclosed in Reference 1. Therefore, even when pieces of data of input video signals correspond to each other in a plurality of lines, input of video signals to a signal line driver circuit cannot be omitted when there is even only one line corresponding to another data among the plurality of lines.

In addition, there is a natural possibility that a plurality of groups of a plurality of lines corresponding to the same data exist such that a group of a plurality of lines having the same data and a group of a plurality of lines having another data exist. In this case, since only comparison of pieces of data corresponding to adjacent lines can be performed by using the technique disclosed in Reference 1, input of video signals to a signal line driver circuit cannot be omitted.

Thus, there is a problem in that power consumption of a signal line driver circuit and power consumption of the entire display device cannot efficiently suppressed even when the technique disclosed in Reference 1 is used.

In addition, there is also a problem in that there is limitation on reduction in power consumption of the entire display device by just devising leading of wirings as disclosed in Reference 2.

In view of the foregoing problems, it is an object of the present invention to provide an active matrix display device in which power consumption of a signal line driver circuit can be suppressed, so that power consumption of the entire appliance can be suppressed.

In a display device of the present invention, a plurality of memory circuits which can write data of a video signal input to a pixel in one line period and can hold the data are provided in a driver circuit. The memory circuit includes a plurality of memory elements and holds data input to pixels for one line in the plurality of memory elements. Then, the data stored in each memory circuit is input to pixels in a corresponding line as a video signals. Since the display device of the present invention includes two or more memory circuits in the driver circuit, pieces of data of video signals corresponding to two or more line periods which appear discontinuously can be concurrently held in the memory circuits. Note that a line period corresponds to a period during which pixels of each line are selected by a scan line driver circuit and signals are input to the selected pixel.

The display device of the present invention includes a memory which can store data of video signals corresponding to a plurality of line periods or a plurality of frame periods, and a data comparison portion which reads data of video signals corresponding to respective line periods from the memory and compares the data with data of video signals corresponding to other line periods.

Then, the data comparison portion controls writing and holding of data in each memory circuit in accordance with the comparison result. Specifically, by comparing the pieces of data of the video signals corresponding to respective line periods, the data comparison portion extracts a plurality of line periods in which pieces of data correspond to each other. Then, after the data comparison portion writes the corresponding data to the memory circuits, the data comparison portion makes the memory circuits hold the data without being rewritten until the video signals having the data are input to the pixels in all the extracted line periods. Further, when input of the video signals in all the extracted line periods is completed, the data comparison portion can rewrite the data stored in the memory circuits into another data.

Note that as the display device of the present invention, an active matrix display device such as a liquid crystal display device, a light-emitting device provided with a light-emitting element typified by an organic light-emitting element (OLED) in each pixel, a DMD (digital micromirror device), a PDP (plasma display panel), or an FED (field emission display) is included in its category. In addition, a passive matrix display device is included in its category.

Various types of switches can be used as a switch shown in this document. An electrical switch, a mechanical switch, and the like are given as examples. That is, any element can be used as long as it can control a current flow, without limiting to a certain element. For example, a transistor (e.g., a bipolar transistor or a MOS transistor), a diode (e.g., a PN diode, a PIN diode, a Schottky diode, an MIM (metal insulator metal) diode, an MIS (metal insulator semiconductor) diode, or a diode-connected transistor), a thyristor, or the like can be used as a switch. Alternatively, a logic circuit combining such elements can be used as a switch.

In the case of using a transistor as a switch, polarity (a conductivity type) of the transistor is not particularly limited because it operates just as a switch. However, a transistor of polarity with smaller off-current is preferably used when off-current is to be suppressed. A transistor provided with an LDD region, a transistor with a multi-gate structure, and the like are given as examples of a transistor with smaller off-current. In addition, it is preferable that an N-channel transistor be used when a potential of a source terminal is closer to a potential of a low-potential-side power supply (e.g., V_(ss), GND, or 0 V), while a P-channel transistor be used when the potential of the source terminal is closer to a potential of a high-potential-side power supply (e.g., V_(dd)). This is because the absolute value of gate-source voltage can be increased when the potential of the source terminal is closer to a potential of a low-potential-side power supply in an N-channel transistor and when the potential of the source terminal is closer to a potential of a high-potential-side power supply in a P-channel transistor. This is also because the transistor does not often perform a source follower operation, so that reduction in output voltage does not often occur.

Note that a CMOS switch using both N-channel and P-channel transistors may be used. By using a CMOS switch, the switch can easily operate as a switch because current can flow when the P-channel transistor or the N-channel transistor is turned on. For example, voltage can be appropriately output regardless of whether voltage of an input signal of the switch is high or low. In addition, since a voltage amplitude value of a signal for turning on or off the switch can be made small, power consumption can be reduced.

When a transistor is used as a switch, the switch includes an input terminal (one of a source terminal and a drain terminal), an output terminal (the other of the source terminal and the drain terminal), and a terminal for controlling electrical conduction (a gate terminal). On the other hand, when a diode is used as a switch, the switch does not have a terminal for controlling electrical conduction in some cases. Therefore, when a diode is used as a switch, the number of wirings for controlling terminals can be more reduced than the case of using a transistor as a switch.

In this document, when it is described that “A and B are connected”, the case where A and B are electrically connected, the case where A and B are functionally connected, and the case where A and B are directly connected are included therein. Here, each of A and B corresponds to an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer). Accordingly, in structures disclosed in this document, another element may be interposed between elements having a connection relation shown in drawings and texts, without limiting to a predetermined connection relation, for example, the connection relation shown in the drawings and the texts.

For example, in the case where A and B are electrically connected, one or more elements which enable electrical connection of A and B (e.g., a switch, a transistor, a capacitor, an inductor, a resistor, and/or a diode) may be provided between A and B. In addition, in the case where A and B are functionally connected, one or more circuits which enable functional connection of A and B (e.g., a logic circuit such as an inverter, a NAND circuit, or a NOR circuit, a signal converter circuit such as a DA converter circuit, an AD converter circuit, or a gamma correction circuit, a potential level converter circuit such as a power supply circuit (e.g., a boosting circuit or a voltage lower control circuit) or a level shifter circuit for changing a potential level of a signal, a voltage source, a current source, a switching circuit, or an amplifier circuit such as a circuit which can increase signal amplitude, the amount of current, or the like (e.g., an operational amplifier, a differential amplifier circuit, a source follower circuit, or a buffer circuit), a signal generating circuit, a memory circuit, and/or a control circuit) may be provided between A and B. Alternatively, in the case where A and B are directly connected, A and B may be directly connected without interposing another element or another circuit therebetween.

When it is described that “A and B are directly connected”, the case where A and B are directly connected (i.e., the case where A and B are connected without interposing another element or another circuit therebetween) and the case where A and B are electrically connected (i.e., the case where A and B are connected by interposing another element or another circuit therebetween) are included therein.

When it is described that “A and B are electrically connected”, the case where A and B are electrically connected (i.e., the case where A and B are connected by interposing another element or another circuit therebetween), the case where A and B are functionally connected (i.e., the case where A and B are functionally connected by interposing another circuit therebetween), and the case where A and B are directly connected (i.e., the case where A and B are connected without interposing another element or another circuit therebetween) are included therein. That is, when it is described that “A and B are electrically connected”, the description is the same as the case where it is explicitly only described that “A and B are connected”.

A display element, a display device which is a device having a display element, a light-emitting element, and a light-emitting device which is a device having a light-emitting element can use various types and can include various elements. For example, as a display element, a display device, a light-emitting element, and a light-emitting device, whose a display medium, contrast, luminance, reflectivity, transmittivity, or the like changes by an electromagnetic action, such as an EL element (e.g., an EL element including organic and inorganic materials, an organic EL element, or an inorganic EL element), an electron emitter, a liquid crystal element, electronic ink, an electrophoresis element, a grating light valve (GLV), a plasma display panel (PDP), a digital micromirror device (DMD), a piezoelectric ceramic display, or a carbon nanotube can be used. Note that display devices using an EL element include an EL display; display devices using an electron emitter include a field emission display (FED), an SED-type flat panel display (SED: Surface-conduction Electron-emitter Display), and the like; display devices using a liquid crystal element include a liquid crystal display (e.g., a transmissive liquid crystal display, a semi-transmissive liquid crystal display, a reflective liquid crystal display, a direct-view liquid crystal display, or a projection liquid crystal display); and display devices using electronic ink or an electrophoresis element include electronic paper.

By using a catalyst (e.g., nickel) in the case of forming microcrystalline silicon, crystallinity can be further improved and a transistor having excellent electric characteristics can be formed. At this time, crystallinity can be improved by performing heat treatment without using a laser. Accordingly, a gate driver circuit (e.g., a scan line driver circuit) and part of a source driver circuit (e.g., an analog switch) can be formed over the same substrate. In addition, in the case of not using a laser for crystallization, crystallinity unevenness of silicon can be suppressed. Therefore, an image having high quality can be displayed.

Note that polycrystalline silicon and microcrystalline silicon can be formed without using a catalyst (e.g., nickel).

A transistor can be formed by using a semiconductor substrate, an SOI substrate, or the like. Thus, a transistor with few variations in characteristics, sizes, shapes, or the like, with high current supply capacity, and with a small size can be formed. By using such a transistor, power consumption of a circuit can be reduced or a circuit can be highly integrated.

A transistor including a compound semiconductor or an oxide semiconductor such as ZnO, a-InGaZnO, SiGe, GaAs, IZO, ITO, or SnO, a thin film transistor obtained by thinning such a compound semiconductor or a oxide semiconductor, or the like can be used. Thus, manufacturing temperature can be lowered and for example, such a transistor can be formed at room temperature. Accordingly, the transistor can be formed directly on a substrate having low heat resistance such as a plastic substrate or a film substrate. Note that such a compound semiconductor or an oxide semiconductor can be used for not only a channel portion of the transistor but also other applications. For example, such a compound semiconductor or an oxide semiconductor can be used as a resistor, a pixel electrode, or a light-transmitting electrode. Further, since such an element can be formed at the same time as the transistor, cost can be reduced.

A transistor formed by using an inkjet method or a printing method, or the like can be used. Accordingly, a transistor can be formed at room temperature, can be formed at a low vacuum, or can be formed using a large substrate. In addition, since the transistor can be formed without using a mask (a reticle), a layout of the transistor can be easily changed. Further, since it is not necessary to use a resist, material cost is reduced and the number of steps can be reduced. Furthermore, since a film is formed only in a necessary portion, a material is not wasted compared with a manufacturing method in which etching is performed after the film is formed over the entire surface, so that cost can be reduced.

A transistor including an organic semiconductor or a carbon nanotube, or the like can be used. Accordingly, such a transistor can be formed using a substrate which can be bent. Therefore, a device using a transistor including an organic semiconductor or a carbon nanotube, or the like can resist a shock.

Further, transistors with various structures can be used. For example, a MOS transistor, a junction transistor, a bipolar transistor, or the like can be used as a transistor described in this document. By using a MOS transistor, the size of the transistor can be reduced. Thus, a large number of transistors can be mounted. By using a bipolar transistor, large current can flow. Thus, a circuit can be operated at high speed.

Note that a MOS transistor, a bipolar transistor, and the like may be formed over one substrate. Thus, reduction in power consumption, reduction in size, high speed operation, and the like can be realized.

Furthermore, various transistors can be used.

A transistor can be formed using various types of substrates. The type of a substrate where a transistor is formed is not limited to a certain type. For example, a single crystalline substrate, an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a paper substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, a rubber substrate, a stainless steel substrate, a substrate including a stainless steel foil, or the like can be used as a substrate where the transistor is formed. Alternatively, a skin (e.g., epidermis or corium) or hypodermal tissue of an animal such as a human being can be used as a substrate where the transistor is formed. In addition, the transistor may be formed using one substrate, and then, the transistor may be transferred to another substrate. A single crystalline substrate, an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a paper substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, a rubber substrate, a stainless steel substrate, a substrate including a stainless steel foil, or the like can be used as a substrate to which the transistor is transferred. Alternatively, a skin (e.g., epidermis or corium) or hypodermal tissue of an animal such as a human being can be used as a substrate to which the transistor is transferred. Further alternatively, the transistor may be formed using one substrate and the substrate may be thinned by polishing. A single crystalline substrate, an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a paper substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, a rubber substrate, a stainless steel substrate, a substrate including a stainless steel foil, or the like can be used as a substrate to be polished. Alternatively, a skin (e.g., epidermis or corium) or hypodermal tissue of an animal such as a human being can be used as a substrate to be polished. By using such a substrate, a transistor with excellent properties or a transistor with low power consumption can be formed, a device with high durability, high heat resistance can be provided, or reduction in weight or thickness can be achieved.

A structure of a transistor can be various modes without limiting to a certain structure. For example, a multi-gate structure having two or more gate electrodes may be used. When the multi-gate structure is used, a structure where a plurality of transistors are connected in series is provided because a structure where channel regions are connected in series is provided. By using the multi-gate structure, off-current can be reduced or the withstand voltage of the transistor can be increased to improve reliability. Alternatively, by using the multi-gate structure, drain-source current does not fluctuate very much even if drain-source voltage fluctuates when the transistor operates in a saturation region, so that a flat slope of voltage-current characteristics can be obtained. By utilizing the flat slope of the voltage-current characteristics, an ideal current source circuit or an active load having a high resistance value can be realized. Accordingly, a differential circuit or a current mirror circuit having excellent properties can be realized. In addition, a structure where gate electrodes are formed above and below a channel may be used. By using the structure where gate electrodes are formed above and below the channel, a channel region is enlarged, so that the amount of current flowing therethrough can be increased or a depletion layer can be easily formed to decrease an S value. When the gate electrodes are formed above and below the channel, a structure where a plurality of transistors are connected in parallel is provided.

Further, a structure where a gate electrode is formed above a channel formation region, a structure where a gate electrode is formed below a channel formation region, a staggered structure, an inversely staggered structure, a structure where a channel formation region is divided into a plurality of regions, or a structure where channel formation regions are connected in parallel or in series can be used. In addition, a source electrode or a drain electrode may overlap with a channel formation region (or part of it). By using the structure where the source electrode or the drain electrode may overlap with the channel formation region (or part of it), the case can be prevented in which electric charges are accumulated in part of the channel formation region, which would result in an unstable operation. Further, an LDD region may be provided. By providing the LDD region, off-current can be reduced or the withstand voltage of the transistor can be increased to improve reliability. Alternatively, by providing the LDD region, drain-source current does not fluctuate very much even if drain-source voltage fluctuates when the transistor operates in the saturation region, so that a flat slope of voltage-current characteristics can be obtained.

Various types of transistors can be used for a transistor in this document and the transistor can be formed using various types of substrates. Accordingly, all of circuits which are necessary to realize a predetermined function may be formed using the same substrate. For example, all of the circuits which are necessary to realize the predetermined function may be formed using a glass substrate, a plastic substrate, a single crystalline substrate, an SOI substrate, or any other substrate. When all of the circuits which are necessary to realize the predetermined function are formed using the same substrate, cost can be reduced by reduction in the number of component parts or reliability can be improved by reduction in the number of connections to circuit components. Alternatively, part of the circuits which are necessary to realize the predetermined function may be formed using one substrate and another part of the circuits which are necessary to realize the predetermined function may be formed using another substrate. That is, not all of the circuits which are necessary to realize the predetermined function are required to be formed using the same substrate. For example, part of the circuits which are necessary to realize the predetermined function may be formed with transistors using a glass substrate and another part of the circuits which are necessary to realize the predetermined function may be formed using a single crystalline substrate, so that an IC chip formed by a transistor using the single crystalline substrate may be connected to the glass substrate by COG (chip on glass) and the IC chip may be provided over the glass substrate. Alternatively, the IC chip may be connected to the glass substrate by TAB (tape automated bonding) or a printed wiring board. When part of the circuits are formed using the same substrate in this manner, cost can be reduced by reduction in the number of component parts or reliability can be improved by reduction in the number of connections to circuit components. In addition, for example, by forming a portion with high driving voltage or a portion with high driving frequency, which consumes large power, using a single crystalline substrate and using an IC chip formed by the circuit instead of forming such a portion using the same substrate, increase in power consumption can be prevented.

Note that one pixel corresponds to one element whose brightness can be controlled in this document. Therefore, for example, one pixel corresponds to one color element and brightness is expressed with the one color element. Accordingly, in the case of a color display device having color elements of R (red), G (green), and B (blue), a minimum unit of an image is formed of three pixels of an R pixel, a G pixel, and a B pixel. Note that the color elements are not limited to three colors, and color elements of more than three colors may be used or a color other than RGB may be used. For example, RGBW (W corresponds to white) may be used by adding white. In addition, one or more colors of yellow, cyan, magenta emerald green, vermilion, and the like may be added to RGB. Further, a color similar to at least one of R, G and B may be added to RGB. For example, R, G, B1, and B2 may be used. Although both B1 and B2 are blue, they have slightly different frequency. Similarly, R1, R2, G, and B may be used. By using such color elements, display which is closer to the real object can be performed or power consumption can be reduced. Alternatively, as another example, in the case of controlling brightness of one color element by using a plurality of regions, one region may correspond to one pixel. Therefore, for example, in the case of performing area ratio gray scale display or the case of including a subpixel, a plurality of regions which control brightness are provided in each color element and gray scales are expressed with the whole regions. In this case, one region which controls brightness may correspond to one pixel. Thus, in that case, one color element includes a plurality of pixels. Alternatively, even when the plurality of regions which control brightness are provided in one color element, these regions may be collected as one pixel. Thus, in that case, one color element includes one pixel. In that case, one color element includes one pixel. In the case where brightness is controlled in a plurality of regions in each color element, regions which contribute to display have different area dimensions depending on pixels in some cases. In addition, in the plurality of regions which control brightness in each color element, signals supplied to each of the plurality of regions may be slightly varied to widen a viewing angle. That is, potentials of pixel electrodes included in the plurality of regions provided in each color element may be different from each other. Accordingly, voltage applied to liquid crystal molecules are varied depending on the pixel electrodes. Therefore, the viewing angle can be widened.

When it is described that “one pixel (for three colors)”, it corresponds to the case where three pixels of R, G, and B are considered as one pixel. Meanwhile, when it is described that “one pixel (for one color)”, it corresponds to the case where the plurality of regions are provided in each color element and collectively considered as one pixel.

In this document, pixels are provided (arranged) in matrix in some cases. Here, description that pixels are provided (arranged) in matrix includes the case where the pixels are arranged in a straight line and the case where the pixels are arranged in a jagged line, in a longitudinal direction or a lateral direction. Thus, for example, in the case of performing full color display with three color elements (e.g., RGB), the following cases are included therein: the case where the pixels are arranged in stripes and the case where dots of the three color elements are arranged in a delta pattern. In addition, the case is also included therein in which dots of the three color elements are provided in Bayer arrangement. Note that the color elements are not limited to three colors, and color elements of more than three colors may be used. RGBW (W corresponds to white), RGB plus one or more of yellow, cyan, magenta, and the like, or the like is given as an example. Further, the sizes of display regions may be different between respective dots of color elements. Thus, power consumption can be reduced or the life of a display element can be prolonged.

In this document, an active matrix method in which an active element is included in a pixel or a passive matrix method in which an active element is not included in a pixel can be used.

In an active matrix method, as an active element (a non-linear element), not only a transistor but also various active elements (non-linear elements) can be used. For example, an MIM (metal insulator metal), a TFD (thin film diode), or the like can also be used. Since such an element has few number of manufacturing steps, manufacturing cost can be reduced or yield can be improved. Further, since the size of the element is small, the aperture ratio can be improved, so that power consumption can be reduced or high luminance can be achieved.

As a method other than an active matrix method, a passive matrix method in which an active element (a non-linear element) is not used can also be used. Since an active element (a non-linear element) is not used, manufacturing steps is few, so that manufacturing cost can be reduced or the yield can be improved. Further, since an active element (a non-linear element) is not used, the aperture ratio can be improved, so that power consumption can be reduced or high luminance can be achieved.

A transistor is an element having at least three terminals of a gate, a drain, and a source. The transistor has a channel formation region between a drain region and a source region, and current can flow through the drain region, the channel formation region, and the source region. Here, since the source and the drain of the transistor may change depending on the structure, the operating condition, and the like of the transistor, it is difficult to define which is a source or a drain. Therefore, in this document, a region functioning as a source and a drain may not be called the source or the drain. In such a case, one of the source and the drain may be referred to as a first terminal and the other thereof may be referred to as a second terminal, for example. Alternatively, one of the source and the drain may be referred to as a first electrode and the other thereof may be referred to as a second electrode. Further alternatively, one of the source and the drain may be referred to as a source region and the other thereof may be called a drain region.

A transistor may be an element having at least three terminals of a base, an emitter, and a collector. In this case also, one of the emitter and the collector may be similarly called a first terminal and the other terminal may be called a second terminal.

A gate corresponds to all or part of a gate electrode and a gate wiring (also referred to as a gate line, a gate signal line, a scan line, a scan signal line, or the like). A gate electrode corresponds to a conductive film which overlaps with a semiconductor which forms a channel formation region with a gate insulating film interposed therebetween. Note that part of the gate electrode overlaps with an LDD (lightly doped drain) region, the source region, or the drain region with the gate insulating film interposed therebetween in some cases. A gate wiring corresponds to a wiring for connecting a gate electrode of each transistor to each other, a wiring for connecting a gate electrode of each pixel to each other, or a wiring for connecting a gate electrode to another wiring.

However, there is a portion (a region, a conductive film, a wiring, or the like) which functions as both a gate electrode and a gate wiring. Such a portion (a region, a conductive film, a wiring, or the like) may be called either a gate electrode or a gate wiring. That is, there is a region where a gate electrode and a gate wiring cannot be clearly distinguished from each other. For example, in the case where a channel formation region overlaps with part of an extended gate wiring, the overlapped portion (region, conductive film, wiring, or the like) functions as both a gate wiring and a gate electrode. Accordingly, such a portion (a region, a conductive film, a wiring, or the like) may be called either a gate electrode or a gate wiring.

A portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a gate electrode, forms the same island as the gate electrode, and is connected to the gate electrode may also be called a gate electrode. Similarly, a portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a gate wiring, forms the same island as the gate wiring, and is connected to the gate wiring may also be called a gate wiring. In a strict detect, such a portion (a region, a conductive film, a wiring, or the like) does not overlap with a channel formation region or does not have a function of connecting the gate electrode to another gate electrode in some cases. However, there is a portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a gate electrode or a gate wiring, forms the same island as the gate electrode or the gate wiring, and is connected to the gate electrode or the gate wiring. Thus, such a portion (a region, a conductive film, a wiring, or the like) may also be called either a gate electrode or a gate wiring.

In a multi-gate transistor, for example, a gate electrode is often connected to another gate electrode by using a conductive film which is formed using the same material as the gate electrode. Since such a portion (a region, a conductive film, a wiring, or the like) is a portion (a region, a conductive film, a wiring, or the like) for connecting the gate electrode to another gate electrode, it may be called a gate wiring, and it may also be called a gate electrode because a multi-gate transistor can be considered as one transistor. That is, a portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a gate electrode or a gate wiring, forms the same island as the gate electrode or the gate wiring, and is connected to the gate electrode or the gate wiring may be called either a gate electrode or a gate wiring. In addition, for example, part of a conductive film which connects the gate electrode and the gate wiring and is formed using a material which is different from that of the gate electrode or the gate wiring may also be called either a gate electrode or a gate wiring.

A gate terminal corresponds to part of a portion (a region, a conductive film, a wiring, or the like) of a gate electrode or a portion (a region, a conductive film, a wiring, or the like) which is electrically connected to the gate electrode.

When a wiring is called a gate wiring, a gate line, a gate signal line, a scan line, a scan signal line, there is the case in which a gate of a transistor is not connected to a wiring. In this case, the gate wiring, the gate line, the gate signal line, the scan line, or the scan signal line corresponds to a wiring formed in the same layer as the gate of the transistor, a wiring formed using the same material of the gate of the transistor, or a wiring formed at the same time as the gate of the transistor in some cases. As examples, a wiring for storage capacitance, a power supply line, a reference potential supply line, and the like can be given.

A source corresponds to all or part of a source region, a source electrode, and a source wiring (also referred to as a source line, a source signal line, a data line, a data signal line, or the like). A source region corresponds to a semiconductor region including a large amount of p-type impurities (e.g., boron or gallium) or n-type impurities (e.g., phosphorus or arsenic). Therefore, a region including a small amount of p-type impurities or n-type impurities, namely, an LDD (lightly doped drain) region is not included in the source region. A source electrode is part of a conductive layer formed using a material different from that of a source region, and electrically connected to the source region. However, there is the case where a source electrode and a source region are collectively called a source electrode. A source wiring is a wiring for connecting a source electrode of each transistor to each other, a wiring for connecting a source electrode of each pixel to each other, or a wiring for connecting a source electrode to another wiring.

However, there is a portion (a region, a conductive film, a wiring, or the like) functioning as both a source electrode and a source wiring. Such a portion (a region, a conductive film, a wiring, or the like) may be called either a source electrode or a source wiring. That is, there is a region where a source electrode and a source wiring cannot be clearly distinguished from each other. For example, in the case where a source region overlaps with part of an extended source wiring, the overlapped portion (region, conductive film, wiring, or the like) functions as both a source wiring and a source electrode. Accordingly, such a portion (a region, a conductive film, a wiring, or the like) may be called either a source electrode or a source wiring.

A portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a source electrode, forms the same island as the source electrode, and is connected to the source electrode, or a portion (a region, a conductive film, a wiring, or the like) which connects a source electrode and another source electrode may also be called a source electrode. Further, a portion which overlaps with a source region may be called a source electrode. Similarly, a portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a source wiring, forms the same island as the source wiring, and is connected to the source wiring may also be called a source wiring. In a strict detect, such a portion (a region, a conductive film, a wiring, or the like) does not have a function of connecting the source electrode to another source electrode in some cases. However, there is a portion (a region, a conductive film, a wiring, or the like) which is formed using the same material as a source electrode or a source wiring, forms the same island as the source electrode or the source wiring, and is connected to the source electrode or the source wiring. Thus, such a portion (a region, a conductive film, a wiring, or the like) may also be called either a source electrode or a source wiring.

For example, part of a conductive film which connects a source electrode and a source wiring and is formed using a material which is different from that of the source electrode or the source wiring may be called either a source electrode or a source wiring.

A source terminal corresponds to a source region, a source electrode, or a portion (a region, a conductive film, a wiring, or the like) which is electrically connected to the source electrode.

When a wiring is called a source wiring, a source line, a source signal line, a data line, a data signal line, there is the case in which a source (a drain) of a transistor is not connected to a wiring. In this case, the source wiring, the source line, the source signal line, the data line, or the data signal line corresponds to a wiring formed in the same layer as the source (the drain) of the transistor, a wiring formed using the same material of the source (the drain) of the transistor, or a wiring formed at the same time as the source (the drain) of the transistor in some cases. As examples, a wiring for storage capacitance, a power supply line, a reference potential supply line, and the like can be given.

The same can be said for a drain.

A semiconductor device corresponds to a device having a circuit including a semiconductor element (e.g., a transistor, a diode, or thyristor). The semiconductor device may also include all devices that can function by utilizing semiconductor characteristics. In addition, the semiconductor device corresponds to a device having a semiconductor material.

A display element corresponds to an optical modulation element, a liquid crystal element, a light-emitting element, an EL element (an organic EL element, an inorganic EL element, or an EL element including organic and inorganic materials), an electron emitter, an electrophoresis element, a discharging element, a light-reflective element, a light diffraction element, a digital micro device (DMD), or the like. Note that the present invention is not limited to this.

A display device corresponds to a device having a display element. The display device may include a plurality of pixels each having a display element. Note that that the display device may also include a peripheral driver circuit for driving the plurality of pixels. The peripheral driver circuit for driving the plurality of pixels may be formed over the same substrate as the plurality of pixels. The display device may also include a peripheral driver circuit provided over a substrate by wire bonding or bump bonding, namely, an IC chip connected by chip on glass (COG) or an IC chip connected by TAB or the like. Further, the display device may also include a flexible printed circuit (an FPC) to which an IC chip, a resistor, a capacitor, an inductor, a transistor, or the like is attached. Note also that the display device includes a printed wiring board (a PWB) which is connected through a flexible printed circuit (an FPC) and to which an IC chip, a resistor, a capacitor, an inductor, a transistor, or the like is attached. The display device may also include an optical sheet such as a polarizing plate or a retardation plate. The display device may also include a lighting device, a housing, an audio input and output device, a light sensor, or the like. Here, a lighting device such as a backlight unit may include a light guide plate, a prism sheet, a diffusion sheet, a reflective sheet, a light source (e.g., an LED or a cold cathode fluorescent lamp), a cooling device (e.g., a water cooling device or an air cooling device), or the like.

A lighting device corresponds to a device having a backlight unit, a light guide plate, a prism sheet, a diffusion sheet, a reflective sheet, or a light source (e.g., an LED, a cold cathode fluorescent lamp, or a hot cathode fluorescent lamp), a cooling device, or the like.

A light-emitting device corresponds to a device having a light-emitting element and the like. In the case of including a light-emitting element as a display element, the light-emitting device is one of specific examples of a display device.

A reflective device corresponds to a device having a light-reflective element, a light diffraction element, light-reflective electrode, or the like.

A liquid crystal display device corresponds to a display device including a liquid crystal element. Liquid crystal display devices include a direct-view liquid crystal display, a projection liquid crystal display, a transmissive liquid crystal display, a reflective liquid crystal display, a semi-transmissive liquid crystal display, and the like.

A driving device corresponds to a device having a semiconductor element, an electric circuit, or an electronic circuit. For example, a transistor which controls input of a signal from a source signal line to a pixel (also referred to as a selection transistor, a switching transistor, or the like), a transistor which supplies voltage or current to a pixel electrode, a transistor which supplies voltage or current to a light-emitting element, and the like are examples of the driving device. A circuit which supplies a signal to a gate signal line (also referred to as a gate driver, a gate line driver circuit, or the like), a circuit which supplies a signal to a source signal line (also referred to as a source driver, a source line driver circuit, or the like) are also examples of the driving device.

A display device, a semiconductor device, a lighting device, a cooling device, a light-emitting device, a reflective device, a driving device, and the like overlap with each other in some cases. For example, a display device includes a semiconductor device and a light-emitting device in some cases. Alternatively, a semiconductor device includes a display device and a driving device in some cases.

In this document, when it is described that “B is formed on A” or “B is formed over A”, it does not necessarily mean that B is formed in direct contact with A. The description includes the case where A and B are not in direct contact with each other, i.e., the case where another object is interposed between A and B. Here, each of A and B corresponds to an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer).

Accordingly, for example, when it is described that a layer B is formed on (or over) a layer A, it includes both the case where the layer B is formed in direct contact with the layer A, and the case where another layer (e.g., a layer C or a layer D) is formed in direct contact with the layer A and the layer B is formed in direct contact with the layer C or D. Note that another layer (e.g., a layer C or a layer D) may be a single layer or a plurality of layers.

Similarly, when it is described that B is formed above A, it does not necessarily mean that B is formed in direct contact with A, and another object may be interposed therebetween. Thus, for example, when it is described that a layer B is formed above a layer A, it includes both the case where the layer B is formed in direct contact with the layer A, and the case where another layer (e.g., a layer C or a layer D) is formed in direct contact with the layer A and the layer B is formed in direct contact with the layer C or D. Note that another layer (e.g., a layer C or a layer D) may be a single layer or a plurality of layers.

Note that when it is described that B is formed in direct contact with A, it includes not the case where another object is interposed between A and B but the case where B is formed in direct contact with A.

Note that the same can be said when it is described that B is formed below or under A.

In this document, when an object is explicitly described in a singular form, the object is preferably singulal Note that the present invention is not limited to this, and the object can be plural. Similarly, when an object is explicitly described in a plural form, the object is preferably plural. Note that the present invention is not limited to this, and the object can be singular.

Since the display device of the present invention includes a plurality of memory circuits in a driver circuit, pieces of data of video signals corresponding to a plurality of line periods can be held concurrently. Therefore, even when there are a plurality of line periods each having the same data and there is a line period corresponding to another data among the plurality of line periods, the corresponding data and another data can be held in different memory circuits. Thus, in the memory circuit in which the corresponded data is held, it is not necessary to rewrite data until the plurality of line periods are completed. That is, input of video signals to a signal line driver circuit, sampling of the video signals in the signal line driver circuit, and writing of data of the sampled video signals to a memory circuit can be performed at one time during the plurality of line periods.

Therefore, even when a plurality of line periods where pieces of data correspond to each other exist discontinuously, power consumption of the signal line driver circuit can be efficiently suppressed. Further, power consumption which is necessary for input of video signals to the signal line driver circuit can be suppressed, so that power consumption of the entire display device can be suppressed.

In addition, since the display device of the present invention includes the plurality of memory circuits, even when a plurality of groups each having a plurality of line periods where pieces of data correspond to each other exist, pieces of data corresponding to respective groups can be held in different memory circuits. Thus, it is not necessary to rewrite data in the memory circuit where the data is held until all the line periods in the group corresponding to the data are completed. That is, input of video signals to the signal line driver circuit, sampling of the video signals in the signal line driver circuit, and writing of data of the sampled video signals to the memory circuit can be performed at one time during all the line periods in one group.

Therefore, even when a plurality of groups each having a plurality of line periods where pieces of data correspond to each other exist, power consumption of the signal line driver circuit can be efficiently suppressed. Further, power consumption which is necessary for input of video signals to the signal line driver circuit can be suppressed, so that power consumption of the entire display device can be suppressed.

Further, in the display device of the present invention, by storing data of video signals corresponding to a plurality of line periods or a plurality of frame periods in a memory, a data comparison portion can compare data of a video signal corresponding to one line period with data of a video signal corresponding to a plurality of line periods other than one line period. Thus, comparison with not only data corresponding to adjacent line periods but also data corresponding to more line periods can be performed, so that power consumption of the signal line driver circuit can be efficiently suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating a structure of a display device of the present invention;

FIGS. 2A and 2B each illustrate an operation of a signal line driver circuit in a display device of the present invention;

FIGS. 3A and 3B each illustrate an operation of a signal line driver circuit in a display device of the present invention;

FIGS. 4A and 4B each illustrate an operation of a signal line driver circuit in a display device of the present invention;

FIG. 5 is a timing chart illustrating a driving method of a display device of the present invention;

FIG. 6 is a block diagram illustrating a structure of a display device of the present invention;

FIG. 7 is a block diagram illustrating a structure of a data comparison portion;

FIG. 8 is a block diagram illustrating a structure of a data comparison portion;

FIG. 9 is a block diagram illustrating a structure of a display device of the present invention;

FIG. 10 is a block diagram illustrating a structure of a data comparison portion;

FIG. 11 is a block diagram illustrating a structure of a display device of the present invention;

FIG. 12 is a block diagram illustrating a structure of a display device of the present invention;

FIGS. 13A and 13B are timing charts each illustrating timing at which a video signal is input to a pixel portion;

FIG. 14 is a circuit diagram of a signal line driver circuit in a display device of the present invention;

FIG. 15 is a circuit diagram of a signal line driver circuit in a display device of the present invention;

FIGS. 16A and 16B are circuit diagrams each illustrating a structure of a pixel portion of a light-emitting device;

FIG. 17 is a circuit diagram illustrating a structure of a pixel portion of a liquid crystal display device;

FIG. 18A is a top plan view of a display device of the present invention, and FIG. 18B is a cross-sectional view of the display device of the present invention;

FIGS. 19A to 19C each illustrate an electronic device using a display device of the present invention;

FIG. 20 is a circuit diagram of a memory element;

FIG. 21 is a block diagram illustrating a structure of a data comparison portion;

FIG. 22 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 23A and 23B each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 24A and 24B each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIG. 25 illustrates an example of a pixel layout of a display device in accordance with the present invention;

FIGS. 26A and 26B each illustrate an example of a pixel layout of a display device in accordance with the present invention;

FIGS. 27A and 27B each illustrate an example of a pixel layout of a display device in accordance with the present invention;

FIG. 28 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 29A to 29D each illustrate an example of a peripheral component of a display device in accordance with the present invention;

FIG. 30 illustrates an example of a peripheral component of a display device in accordance with the present invention;

FIGS. 31A to 31C each illustrate an example of a circuit structure of a panel of a display device in accordance with the present invention;

FIGS. 32A and 32B each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 33A to 33C each illustrate an example of a driving method of a display device in accordance with the present invention;

FIGS. 34A and 34B each illustrate an example of a circuit structure of a display device in accordance with the present invention;

FIGS. 35A to 35C each illustrate an example of a peripheral component of a display device in accordance with the present invention;

FIGS. 36A and 36B each illustrate an example of a circuit structure of a display device in accordance with the present invention;

FIG. 37 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 38 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIGS. 39A and 39B each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 40A to 40D each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 41A to 41D each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 42A to 42D each illustrate an example of a cross-sectional view of a display device in accordance with the present invention;

FIG. 43 illustrates an example of a top plan view of a display device in accordance with the present invention;

FIGS. 44A to 44D each illustrate an example of a top plan view of a display device in accordance with the present invention;

FIGS. 45A to 45D each illustrate an example of a top plan view of a display device in accordance with the present invention;

FIG. 46A illustrates an example of a pixel layout of a display device in accordance with the present invention, and FIG. 46B illustrates an example of a cross-sectional view thereof;

FIG. 47A illustrates an example of a pixel layout of a display device in accordance with the present invention, and FIG. 47B illustrates an example of a cross-sectional view thereof;

FIG. 48A illustrates an example of a pixel layout of a display device in accordance with the present invention, and FIG. 48B illustrates an example of a cross-sectional view thereof;

FIGS. 49A and 49B each illustrate an example of a timing chart of a display device in accordance with the present invention;

FIGS. 50A and 50B each illustrate an example of a timing chart of a display device in accordance with the present invention;

FIG. 51 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 52 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 53 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 54 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 55 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIGS. 56A to 56G illustrate a manufacturing process of a display device in accordance with the present invention;

FIG. 57 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIG. 58 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIG. 59 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIG. 60 illustrates an example of a cross-sectional view of a display device in accordance with the present invention;

FIGS. 61A to 61C each illustrate an example of a display element of a display device in accordance with the present invention;

FIGS. 62A to 62C each illustrate an example of a display element of a display device in accordance with the present invention;

FIGS. 63A and 63B illustrate an example of a structure of a display device in accordance with the present invention;

FIG. 64 illustrates an example of a structure of a display device in accordance with the present invention;

FIG. 65 illustrates an example of a structure of a display device in accordance with the present invention;

FIG. 66 illustrates an example of a structure of a display device in accordance with the present invention;

FIGS. 67A to 67C each illustrate an example of a structure of a display device in accordance with the present invention;

FIG. 68 illustrates an example of a circuit structure of a display device in accordance with the present invention;

FIG. 69 illustrates an example of a timing chart of a display device in accordance with the present invention;

FIG. 70 illustrates an example of a timing chart of a display device in accordance with the present invention;

FIGS. 71A and 71B each illustrate an example of a driving method of a display device in accordance with the present invention;

FIGS. 72A to 72E each illustrate an example of a display element of a display device in accordance with the present invention;

FIG. 73 illustrates an example of a manufacturing device of a display device in accordance with the present invention;

FIG. 74 illustrates an example of a manufacturing device of a display device in accordance with the present invention;

FIG. 75 illustrates an example of a structure of a display device in accordance with the present invention;

FIG. 76 illustrates an example of a structure of a display device in accordance with the present invention;

FIGS. 77A and 77B each illustrate an example of a structure of a display device in accordance with the present invention;

FIGS. 78A and 78B each illustrate an example of a structure of a display device in accordance with the present invention;

FIG. 79 illustrates an example of a structure of a display device in accordance with the present invention;

FIG. 80 illustrates an example of a structure of a display device in accordance with the present invention;

FIGS. 81A to 81H each illustrate an electronic device using a display device in accordance with the present invention;

FIG. 82 illustrates an electronic device using a display device in accordance with the present invention;

FIG. 83 illustrates an electronic device using a display device in accordance with the present invention;

FIG. 84 illustrates an electronic device using a display device in accordance with the present invention;

FIG. 85 illustrates an electronic device using a display device in accordance with the present invention;

FIGS. 86A and 86B each illustrate an electronic device using a display device in accordance with the present invention; and

FIGS. 87A and 87B illustrate an electronic device using a display device in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described by way of embodiment modes and embodiments with reference to the drawings. However, the present invention can be implemented in various different ways and it will be easily understood by those skilled in the art that various changes and modifications are possible. Unless such changes and modifications depart from the spirit and the scope of the present invention, they should be construed as being included therein. Therefore, the present invention should not be construed as being limited to the description of the embodiment modes and embodiments.

Embodiment Mode 1

FIG. 1 is a block diagram of a display device of the present invention. The display device of the present invention includes a pixel portion 100 including a plurality of pixels, a scan line driver circuit 101 which can select a plurality of pixels in each line, and a signal line driver circuit 102 which controls input of a video signal to pixels in a selected line. The signal line driver circuit 102 includes at least a shift register 103, a sampling circuit 104, and a plurality of memory circuits. Each memory circuit includes a plurality of memory elements which can store data input to pixels for one line.

FIG. 1 shows an example in which a first latch 105, a second latch 106, a third latch 107, and a fourth latch 108 are used for the plurality of memory circuits. Note that the number of latches used in the display device of the present invention is not limited to four, and the number of latches may be two or three, or may be five or more.

Next, an operation of the signal line driver circuit 102 is described. A clock signal S-CLK and a start pulse signal S—SP are input to the shift register 103. The shift register 103 generates timing signals, pulses of which are sequentially shifted, in accordance with the clock signal S-CLK and the start pulse signal S—SP, and inputs the timing signals to the sampling circuit 104. The sampling circuit 104 samples video signals for one line period, which are input to the signal line driver circuit 102, in accordance with the input timing signal. Then, when the video signals corresponding to each pixel are sampled, the sampled video signal is input in each time to one or a plurality of the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108 in the lower stage.

Note that in this embodiment mode, an example is described in which a sampled video signal is input in each time to the memory circuit in the lower stage without waiting for completion of one line period; however, the present invention is not limited to this structure. After all the video signals for one line period are sampled, the sampled video signals may be input to the memory circuit in the lower stage all at once.

In addition, video signals may be sampled for one pixel at one time serially after completion of sampling of video signals for another pixel, or pixels in one line may be divided into several groups and video signals may be sampled for each pixel corresponding in one group at the same time.

Writing latch signals WS₁ to WS₄ which control writing of data included in a video signal and reading latch signals RS₁ to RS₄ which control reading of stored data are input to the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108, respectively. Specifically, the writing latch signal WS₁ and the reading latch signal RS₁ are input to the first latch 105. The writing latch signal WS₂ and the reading latch signal RS₂ are input to the second latch 106. The writing latch signal WS₃ and the reading latch signal RS₃ are input to the third latch 107. The writing latch signal WS₄ and the reading latch signal RS₄ are input to the fourth latch 108.

In accordance with the writing latch signals WS₁ to WS₄, data of video signals for one line period, which are input from the signal line driver circuit 102, are written to and stored in the first latch 105, the second latch 106, the third latch 107, or the fourth latch 108. Further, in accordance with the reading latch signals RS₁ to RS₄, the data stored in the first latch 105, the second latch 106, the third latch 107, or the fourth latch 108 is output as a video signal.

Note that although the pixel portion 100 is directly connected to the next stage of the memory circuit in FIG. 1, the present invention is not limited to this structure. A circuit which processes the video signal output from the first latch 105, the second latch 106, the third latch 107, or the fourth latch 108 can be provided in a previous stage of the pixel portion 100. Examples of the circuit which performs signal processing include a buffer which can shape a waveform, a level shifter which can amplify amplitude, and a digital/analog converter circuit which can convert a digital signal into an analog signal.

Then, at the same time as inputting a video signal to the pixel portion 100 from one of the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108, the sampling circuit 104 can sample video signals corresponding to the next line period again. Note that in the present invention, when the same data as the video signal corresponding to the next line period is stored in advance in one of the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108, sampling of the video signal in the sampling circuit 104 can be stopped.

When sampling is stopped, input of pulses of the clock signal S-CLK and the start pulse signal S—SP to the shift register 103 is stopped, and generation of a pulse of the timing signal in the shift register 103 is stopped. Note that in order to stop the generation of a pulse of the timing signal, only input of a pulse of a clock signal S-CLK to the shift register 103 may be stopped, or only input of the pulses of the start pulse signal S—SP to the shift register 103 may be stopped. When output of pulses of a timing signal from the shift register 103 is stopped, the sampling circuit 104 stops sampling of the video signals. Then, in accordance with the reading latch signals RS₁ to RS₄, the same data as the video signals corresponding to the next line period is input as video signals to the pixel portion 100 from one of the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108.

Next, a specific operation of the signal line driver circuit 102 is described using the case where pieces of data of video signals input to pixels in a j-th line, a (j+a)th line, and a (j+b)th line of the pixel portion 100 are the same, as an example.

First, as shown in FIG. 2A, it is assumed that the pixels in the j-th line are selected and data stored in the first latch 105, for example, is input as video signals to the pixels in the j-th line which is selected. Note that the data of the video signals are written to the first latch 105 through a series of operations in the signal line driver circuit 102 in which the shift register 103 generates a timing signal, and the sampling circuit 104 samples the video signals in accordance with a pulse of the timing signal and inputs the sampled video signals to the first latch 105. That is, in order to input the video signals to the pixels in the j-th line, the shift register 103, the sampling circuit 104, and the first latch 105 are driven in the signal line driver circuit 102, as shown in FIG. 2B.

Next, as shown in FIG. 3A, it is assumed that the pixels in the (j+a)th line is selected. Video signals having the same data as that of the video signals input to the j-th line are input to the pixels in the (j+a)th line which is selected. Accordingly, the data stored in the first latch 105 is input as video signals. Note that data of the video signals have already been written to the first latch 105 before the pixels in the j-th line is selected. Therefore, when the data is stored in the first latch 105 after selection of the pixels in the j-th line finishes, writing of the data to the first latch 105 is not necessarily performed again before the pixels in the (j+a)th line are selected. Thus, in order to input video signals to the pixels in the (j+a)th line, it is acceptable as long as only the first latch 105 is driven in the signal line driver circuit 102, as shown in FIG. 3B.

Next, as shown in FIG. 4A, it is assumed that after the pixel in the (j+a)th line is selected and before the pixel in the (j+b)th line is selected, pixels in a line corresponding to another data is selected, and data stored in the third latch 107, for example, is input as video signals to the pixels in the line which is selected. Note that the data of the video signals are written to the third latch 107 through a series of operations in the signal line driver circuit 102 in which the shift register 103 generates a timing signal, and the sampling circuit 104 samples the video signals in accordance with a pulse of the timing signal and inputs the sampled video signals to the third latch 107. That is, in order to input the video signals to the pixels in the line, the shift register 103, the sampling circuit 104, and the third latch 107 are driven in the signal line driver circuit 102, as shown in FIG. 4B.

Note that in the present invention, the data which has already been written can be continuously stored in the first latch 105 while the pixels in the line corresponding to another data are selected. Accordingly, when the pixels in the (j+b)th line is selected, the data stored in the first latch 105 can be input as video signals to the pixels in the (j+b)th line even after selection of the line corresponding to another data finishes. Thus, in order to input the video signals to the pixels in the (j+b)th line, it is acceptable as long as only the first latch 105 is driven in the signal line driver circuit 102, similarly in the case of FIG. 3B.

Next, FIG. 5 shows an example of a timing chart of the clock signal S-CLK and the start pulse signal S—SP which are input to the shift register 103, the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ which are input to the first latch 105, the second latch 106, the third latch 107, and the fourth latch 108, respectively, data (referred to as DATA1) of a video signal output from the sampling circuit 104, and data (referred to as DATA2) of a video signal input to the pixel portion 100, using the display device shown in FIG. 1 as an example. Note that FIG. 5 shows the case that when video signals corresponding to each pixel are sampled by the sampling circuit 104, the sampled video signals are input in each time to the memory circuit in the lower stage without waiting for completion of one line period.

As shown in FIG. 5, in a line period which appears first, a video signal having data denoted by “A” is output from the sampling circuit 104. The video signals having the data “A”, which is output from the sampling circuit 104, are written to the first latch 105 in accordance with a pulse of the writing latch signal WS₁. Note that at this time, other latch circuits may be made to be in a state capable of being written by the writing latch signal. Accordingly, the data “A” can be written to a plurality of latch circuits concurrently.

In a line period which appears next, video signals having data denoted by “B” are output from the sampling circuit 104. The video signals having the data “B”, which is output from the sampling circuit 104, are written to the second latch 106 in accordance with a pulse of the writing latch signal WS₂. The video signals having the data “A” are input to the pixel portion 100 from the first latch 105 in accordance with a pulse of the reading latch signal RS₁.

In a line period which appears next, video signals having data denoted by “C” are output from the sampling circuit 104. The video signals having the data “C”, which is output from the sampling circuit 104, are written to the third latch 107 in accordance with a pulse of the writing latch signal WS₃. The video signals having the data “B” are input to the pixel portion 100 from the second latch 106 in accordance with a pulse of the reading latch signal RS₂.

In a line period which appears next, video signals having data denoted by “D” are output from the sampling circuit 104. The video signals having the data “D”, which is output from the sampling circuit 104, are written to the fourth latch 108 in accordance with a pulse of the writing latch signal WS₄. The video signals having the data “C” are input to the pixel portion 100 from the third latch 107 in accordance with a pulse of the reading latch signal RS₃.

In a line period which appears next, input of one or both of the pulses of the clock signal S-CLK and the start pulse signal S—SP to the shift register 103 is stopped. Thus, generation of a timing signal in the shift register 103 is stopped, so that updating of output of the video signals from the sampling circuit 104 is stopped. Further, the video signals having the data “D” are input to the pixel portion 100 from the fourth latch 108 in accordance with a pulse of the reading latch signal RS₄.

In a line period which appears next, input of one or both of the pulses of the clock signal S-CLK and the start pulse signal S—SP to the shift register 103 has been stopped, subsequently to the previous line period. Thus, generation of the timing signal in the shift register 103 is stopped, so that updating of output of the video signals from the sampling circuit 104 is stopped. Further, the video signals having the data “A” are input to the pixel portion 100 from the first latch 105 in accordance with the pulse of the reading latch signal RS₁.

In a line period which appears next, input of one or both of the pulses of the clock signal S-CLK and the start pulse signal S—SP to the shift register 103 has been stopped, subsequently to the previous line period. Thus, generation of the timing signal in the shift register 103 is stopped, so that updating of output of the video signal from the sampling circuit 104 is stopped. Further, the video signals having the data “B” are input to the pixel portion 100 from the second latch 106 in accordance with the pulse of the reading latch signal RS₂.

In a line period which appears next, input of the pulses of the clock signals S-CLK and the start pulse signals S—SP to the shift register 103 is resumed. Thus, generation of the timing signals in the shift register 103 is also resumed, so that the video signals having data denoted by “E” are output from the sampling circuit 104. The video signals having data “E”, which are output from the sampling circuit 104, are written to the third latch 107 in accordance with the pulses of the writing latch signals WS₃. The video signals having the data “A” are input to the pixel portion 100 from the first latch 105 in accordance with the pulses of the reading latch signals RS₁.

In a line period which appears next, input of one or both of the pulses of the clock signals S-CLK and the start pulse signals S—SP to the shift register 103 is stopped. Thus, generation of the timing signals in the shift register 103 is stopped, so that updating of output of the video signals from the sampling circuit 104 is stopped. Further, the video signals having the data “E” are input to the pixel portion 100 from the third latch 107 in accordance with the pulses of the reading latch signals RS₃.

Note that in FIG. 5, after data of video signals are written to a memory circuit, the written data is input to the pixel portion 100 as video signals in latter periods; however, the present invention is not limited to this configuration. At the same time as writing data of video signals to a memory circuit, the written data may be input to the pixel portion 100 as video signals.

In addition, FIG. 5 illustrates the case that when a video signal corresponding to each pixel is sampled by the sampling circuit 104, the sampled video signal is input in each time to the memory circuit in the lower stage without waiting for completion of one line period; however, the present invention is not limited to this structure. After all the video signals for one line period are sampled, the sampled video signals may be input to the memory circuit in the lower stage all at once. Note that in this case, the sampling circuit 104 is operated by dividing one line period into a period for sampling video signals and a period for outputting the sampled video signals. Then, the sampled video signals are written to the memory circuit only in the latter period.

Since the display device of the present invention includes a plurality of memory circuits in the signal line driver circuit 102, pieces of data of video signals corresponding to a plurality of line periods can be concurrently held. Thus, as shown in FIG. 5, for example, the data “A” and another data can be held in different memory circuits even when a line period corresponding to writing of another data exists during second, sixth, and eighth line periods corresponding to writing of the data “A”. Accordingly, in the memory circuit in which the corresponding data “A” is stored (in FIG. 5, the first latch 105), it is not necessary to rewrite data until all the second, sixth, and eighth line periods end. That is, input of video signals to the signal line driver circuit 102, sampling of the video signal in the signal line driver circuit 102, and writing of data “A” of the sampled video signals can be completed at one time during the second, sixth, and eighth line periods.

Accordingly, in the present invention, power consumption of the signal line driver circuit 102 can be efficiently suppressed even when a plurality of line periods where pieces of data correspond to each other exist discontinuously. Further, power consumption needed for inputting video signals to the signal line driver circuit 102 can be suppressed, so that power consumption of the display device as a whole can be suppressed.

In addition, since the display device of the present invention includes a plurality of memory circuits in the driver circuit, even when a plurality of groups formed of a plurality of line periods where pieces of data correspond to each other exist, for example, a group formed of the second, sixth, and eighth line periods corresponding to the data “A” and a group formed of third, seventh, and tenth line periods corresponding to the data “B”, data corresponding to each group can be held in different memory circuits. Accordingly, in the memory circuits in which the data is held, it is not necessary to rewrite the data until all of the line periods in the group corresponding to the data end. That is, input of a video signal to the signal line driver circuit 102, sampling of the video signal in the signal line driver circuit 102, and writing of data “A” of the sampled video signal can be completed at one time during the line periods in one group.

Accordingly, power consumption of the signal line driver circuit can be efficiently suppressed even when a plurality of groups each formed of a plurality of line periods where pieces of data correspond to each other exist. Further, power consumption needed for inputting video signals to the signal line driver circuit can be suppressed, so that power consumption of the display device as a whole can be suppressed.

Note that FIG. 5 illustrates the case where two groups, for example, the group formed of a plurality of line periods corresponding to the data “A” and the group formed of a plurality of line periods corresponding to the data “B” exist; however, the number of groups is not limited to two. The number of memory circuits is set as appropriate in accordance with the number of groups in which writing of data to the memory circuits should be omitted and timing of writing and reading data in the memory circuit.

The case as shown in FIG. 5, for example, is considered in which there is a gap between timing of writing data of a video signal and timing of reading the data. In this case, line sequential driving in which data is written to all pixels belonging to one line all at once can be performed. Further, in this case, when a plurality of line periods, for example, a line period corresponding to the data “C” and a line period corresponding to the data “D”, each having data which does not correspond to that of the other line periods, continuously appear, a memory circuit for writing non-corresponding data is necessary in addition to a memory circuit for writing corresponding data. Accordingly, the number of memory circuits provided in the signal line driver circuit is preferably the number obtained by adding one to the number of groups.

Alternatively, a structure which is different from FIG. 5, for example, may be employed in which data of a video signal is not written to a memory circuit but input as a video signal to the pixel portion 100 directly from the sampling circuit. In this case, dot sequential driving in which a signal is sequentially written to each pixel can be performed. At this time, the signal line driver circuit 102 is not necessarily provided with a memory circuit for writing non-corresponding data, and it is acceptable as long as the signal line driver circuit 102 is provided with a memory circuit for writing corresponding data. Accordingly, in this case, the number of memory circuits provided in the signal line driver circuit 102 is preferably the same as the number of groups.

Note that the signal line driver circuit 102 may be controlled so as to write data of a video signal to a memory circuit and input the written data as a video signal to the pixel portion 100 at the same time, which is different from FIG. 5. In this case, both writing and reading of data to/from the memory circuit can be performed in one line period. Accordingly, in a structure capable of performing line sequential driving, the signal line driver circuit 102 can perform dot sequential driving.

As the number of memory circuits is increased, the number of writing of data to the memory circuits can be further reduced, which leads to reduction in power consumption of the signal line driver circuit. On the other hand, by suppressing the number of memory circuits, a ratio of the area of a substrate occupied by the signal line driver circuit can be decreased.

In addition, this embodiment mode shows a display device including one signal line driver circuit and one scan line driver circuit; however, the present invention is not limited to this structure. Two or more signal line driver circuits may be provided, or two or more scan line driver circuits may be provided.

When a plurality of signal line driver circuits are provided, sampling of video signals can be sequentially performed by the plurality of signal line driver circuits. Thus, driving frequency of the signal line driver circuits can be reduced, and power consumption can also be reduced. When a plurality of scan line driver circuits are provided, a plurality of lines can be selected at the same time and pieces of data can be concurrently written; thus, one line period can be extended. Accordingly, since driving frequency of the signal line driver circuit can be reduced, power consumption can also be reduced.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 2

FIG. 6 is a block diagram of a display device of the present invention. The display shown in FIG. 6 includes a memory for storing video signals and a data comparison portion 110 which compares video signals stored in the memory in corresponding line periods in addition to the display device shown in FIG. 1. FIG. 6 shows an example in which a RAM (random access memory) 111 and a RAM 112 are used as the memory for storing the video signals. For the RAMs 111 and 112, various RAMs such as an SDRAM (synchronous dynamic random access memory), a DRAM (dynamic random access memory), and an SRAM (static random access memory) can be used.

In addition, the display device of the present invention may include a control circuit 113 and a data format circuit 114 as shown in FIG. 6. A clock signal CLK and a signal which is used for reconstructing a screen in the pixel portion 100, such as a horizontal synchronization signal Hsync used for horizontal synchronization or a vertical synchronization signal Vsync used for vertical synchronization are input to the control circuit 113. The control circuit 113 can generate the clock signal S-CLK and the start pulse signal S—SP for controlling operation of the signal line driver circuit 102, and a clock signal G-CLK and a start pulse signal G-SP for controlling operation of the scan line driver circuit 101 by using the input signals.

The data format circuit 114 can generate a video signal which meets specifications of the pixel portion 100, the scan line driver circuit 101, and the signal line driver circuit 102 in accordance with the signal from the control circuit 113 by using input image data.

The video signal output from the data format circuit 114 is stored in the RAM 111 or the RAM 112. This embodiment mode describes the case where video signals corresponding to one frame period is stored in each of the RAM 111 and the RAM 112; however, the present invention is not limited to this structure. Video signals corresponding to a period longer than one frame period or video signals corresponding to a period shorter than one frame period may be stored in each of the RAM 111 and the RAM 112.

In addition, this embodiment mode shows an example in which two RAMs are used for the memories; however, the number of memories is not limited to two in the present invention. For example, video signals may be stored in three or more memories, or one memory. Note that when a plurality of memories are employed, writing of video signals to the memories and reading of video signals from the memories can be performed at the same time, so that driving speed of the data comparison portion 110 can be further increased. Thus, comparison of much more data can be performed, and power consumption can be more efficiently suppressed.

Information on corresponding line periods is added to the video signals stored in the RAM 111 and the RAM 112 by the data format circuit 114. The data comparison portion 110 reads pieces of data of the video signals corresponding to respective line periods from the RAM 111 or the RAM 112, compares the pieces of data, and extracts a plurality of line periods where pieces of data correspond to each other. Then, the data comparison portion 110 generates the writing latch signals WS₁ to WS₄ so that the corresponding data is written to one of memory circuits in accordance with timing of a line period which appears first among the plurality of line periods and the data written to the memory circuits is stored in the memory circuits until a line period which appears last among the plurality of line periods ends. Further, the data comparison portion 110 generates the reading latch signals RS₁ to RS₄ so that the data written to the memory circuits are input as video signals to the pixel portion 100 in a plurality of line periods where pieces of data correspond to each other. The writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ which are generated are input from the data comparison portion 110 to the memory circuits in the signal line driver circuit 102.

In addition, the data comparison portion 110 processes the start pulse signal S—SP and the clock signal S-CLK input to the data comparison portion 110 so that output of pulses is stopped in a period during which writing is preformed in a plurality of lines in accordance with timing at which a plurality of line periods appear so that sampling of video signals in the signal line driver circuit 102 can be completed at one time since the first line period appears and until the last line period ends through, in other words, in the plurality of line periods where pieces of data of video signals correspond to each other. Then, the data comparison portion 110 inputs the processed start pulse signal S—SP and the clock signal S-CLK to the shift register 103 in the signal line driver circuit 102. With the aforementioned structure, sampling of video signals in the sampling circuit 104 can be performed just once during the plurality of line periods.

Further, the data comparison portion 110 controls output of video signals in accordance with timing at which the plurality of line periods appear so that input of video signals to the signal line driver circuit 102 can be completed at one time during the plurality of line periods where pieces of data of video signals correspond to each other.

FIG. 7 shows an example of a specific structure of the data comparison portion 110. In a block diagram shown in FIG. 7, the data comparison portion 110 includes a comparator 115, an address memory 116, an arithmetic circuit 117, a PLL (phase locked loop) circuit 118, and a signal control circuit 119.

The arithmetic circuit 117 reads a video signal from the RAM 111 or the RAM 112. For example, it is assumed that the arithmetic circuit 117 reads video signals in a j-th line period and video signals in a (j+a)th line period. The arithmetic circuit 117 controls the comparator 115 so as to compare pieces of data of the read video signals. When the pieces of data of the video signals correspond to each other as a result of comparison by the comparator 115, the arithmetic circuit 117 makes the address memory 116 store information on line periods the pieces of data of which correspond to each other.

The arithmetic circuit 117 needs to be driven at higher speed as the number of line periods in which pieces of data should be compared is increased. For example, when data corresponding to one line period is compared with data corresponding to N pieces of line periods, the frequency of a clock signal controlling driving of the arithmetic circuit 117 is preferably N times the frequency of the clock signal S-CLK. Accordingly, in the data comparison portion 110 shown in FIG. 7, the frequency of the input clock signals S-CLK is converted into N times by the PLL circuit 118 and the clock signals S-CLK with the converted frequency are input to the arithmetic circuit 117.

Note that a clock signal for controlling driving of the arithmetic circuit 117 may be separately generated in the control circuit 113, which is not shown in FIG. 7, and input to the arithmetic circuit 117. In this case, the frequency of the clock signal for controlling driving of the arithmetic circuit 117 can be controlled by the control circuit 113; thus, the PLL circuit 118 is not necessarily provided.

Further, the arithmetic circuit 117 reads information on line periods the pieces of data of which correspond to each other from the address memory 116. Then, the arithmetic circuit 117 controls the signal control circuit 119 so that the start pulse signal S—SP and the clock signal S-CLK which are input to the data comparison portion 110 are processed in accordance with timing at which the line periods appear. The processed start pulse signal S—SP and clock signal S-CLK are input from the signal control circuit 119 to the signal line driver circuit 102.

Moreover, the arithmetic circuit 117 controls the signal control circuit 119 so that the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ are generated in accordance with the timing at which the line periods appear. The generated writing latch signals WS₁ to WS₄ and reading latch signals RS₁ to RS₄ are input from the signal control circuit 119 to the signal line driver circuit 102.

Furthermore, the arithmetic circuit 117 controls input of video signals from the signal control circuit 119 to the signal line driver circuit 102 in accordance with the timing at which the line periods appear. For example, as shown in FIG. 7, in the j-th line period, video signals in the j-th line period and video signals in a (j+p)th line period are input to the arithmetic circuit 117 and pieces of data are compared. Then, regardless of the result of comparison, the arithmetic circuit 117 controls the signal control circuit 119 so that the video signals in the j-th line period are output to the signal line driver circuit 102. Next, as shown in FIG. 21, when the data of the video signals in the j-th line period and the data of the video signals in the (j+p)th line period correspond to each other, the arithmetic circuit 117 stops output of the video signals to the signal line driver circuit 102 in the (j+p)th line period. On the other hand, when the data of the video signals in the j-th line period and the data of the video signals in the (j+p)th line period do not correspond to each other, the arithmetic circuit 117 controls the signal control circuit 119 so that the video signals in the (j+p)th line period is output to the signal line driver circuit 102. Note that in the (j+p)th line period, the video signals in the (j+p)th line period and video signals in a (j+q)th period (p<q) are input to the arithmetic circuit 117 and pieces of data are compared.

Note that the case is assumed in which a plurality of groups each including a plurality of line periods corresponding to the same data exist and the number of groups is larger than the number of memory circuits which can store data. In this case, a group in which data is written to a memory circuit earlier may be preceded, and in the other groups, a normal operation, that is, rewriting of data of video signals in the memory circuit may be performed in each line period. Alternatively, even when another data has been written to the memory circuit earlier and a line period belonging to another group appears later, data corresponding to another group may be written so that the group is preceded.

Alternatively, data of a group in which the number of line periods corresponding to the same data is large may be written to the memory circuit so that the group is preceded. FIG. 8 shows a structure of the data comparison portion 110 in the case where a plurality of groups each including a plurality of line periods corresponding to the same data exist and priority is given to the groups in accordance with the number of line periods.

In a block diagram shown in FIG. 8, the data comparison portion 110 includes a counter 120 in addition to the comparator 115, the address memory 116, the arithmetic circuit 117, the PLL (phase locked loop) circuit 118, and the signal control circuit 119. In the data comparison portion 110 shown in FIG. 8, when pieces of data correspond to each other as a result of comparison in the comparator 115, information on the fact that the pieces of data correspond to each other is transmitted to the counter 120. When the counter 120 counts the number of line periods where pieces of data correspond to each other based on the information, the arithmetic circuit 117 sets priorities to each group in accordance with the number of line periods. Then, the arithmetic circuit 117 controls the signal control circuit 119 so that the signal control circuit 119 generates the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ in order that data of a group more highly preceded is preferentially stored in a memory circuit.

Note that in the display device of the present invention shown in FIG. 6, signal processing of the start pulse signal S—SP and the clock signal S-CLK and generation of the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ are all performed in the data comparison portion 110; however, these operations may be performed in the control circuit 113. Next, an operation of the data comparison portion 110 in the display device shown in FIG. 6 is described with reference to FIG. 9 in the case where signal processing of the start pulse signal S—SP and the clock signal S-CLK and generation of the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ are performed in the control circuit 113.

In a block diagram shown in FIG. 9, the data comparison portion 110 reads pieces of data of video signals corresponding to each line period from the RAM 111 or the RAM 112, compares the pieces of data, and extracts a plurality of line periods where pieces of data of video signals correspond to each other. Then, a signal including information on which line periods are extracted is input to the control circuit 113 as a timing control signal. Further, the data comparison portion 110 controls output of video signals in accordance with timing at which the plurality of line periods appear so that input of video signals to the signal line driver circuit 102 can be completed at one time during the plurality of line periods where the pieces of data of video signals correspond to each other.

The control circuit 113 generates the writing latch signals WS₁ to WS₄ in accordance with the input timing control signal so that the corresponding data is written to one of memory circuits in accordance with timing of a line period which appears first among the plurality of line periods where the pieces of data correspond to each other and the data written to the memory circuit is stored in the memory circuit until a line period which appears last among the plurality of line periods ends. Further, the control circuit 113 generates the reading latch signals RS₁ to RS₄ in accordance with the timing control signal input thereto so that the data written to the memory circuit is input as video signals to the pixel portion 100 in the plurality of line periods where the pieces of data correspond to each other. The writing latch signals WS₁ to WS₄ and reading latch signals RS₁ to RS₄ which are generated are input from the control circuit 113 to the memory circuit in the signal line driver circuit 102.

The clock signal CLK and a signal used for reconstructing a screen in the pixel portion 100, such as the horizontal synchronization signal Hsync used for horizontal synchronization or the vertical synchronization signal Vsync used for vertical synchronization are input to the control circuit 113. The control circuit 113 can generate the clock signal S-CLK and the start pulse signal S—SP for controlling the operation of the signal line driver circuit 102, the clock signal G-CLK and the start pulse signal G-SP for controlling the operation of the scan line driver circuit 101, and a clock signal A-CLK for controlling the driving of the data comparison portion 110 by using the input signals. The clock signal A-CLK is output from the control circuit 113 to the data comparison portion 110. The control circuit 113 processes the start pulse signal S—SP and the clock signal S-CLK in accordance with the input timing control signal so that sampling of video signals in the signal line driver circuit 102 can be completed at one time during a plurality of line periods where pieces of data of video signals correspond to each other, and inputs the processed start pulse signal S—SP and clock signal S-CLK to the shift register 103 in the signal line driver circuit 102. With the aforementioned structure, sampling of video signals in the sampling circuit 104 can be performed just once through a plurality of line periods.

Next, an operation of the data comparison portion 110 shown in FIGS. 7 and 8 is described with reference to FIG. 10 in the case where signal processing of the start pulse signal S—SP and the clock signal S-CLK and generation of the writing latch signals WS₁ to WS₄ and the reading latch signals RS₁ to RS₄ are performed in the control circuit 113. Note that FIG. 10 shows the operation of the data comparison portion 110 shown in FIG. 8 as an example; however, the operation of the data comparison portion 110 shown in FIG. 7 can be similarly described.

In FIG. 10, the arithmetic circuit 117 reads information on line periods where the pieces of data correspond to each other from the address memory 116. Then, the arithmetic circuit 117 controls the signal control circuit 119 so that the signal control circuit 119 generates a timing control signal including information on which line periods are extracted based on the information. The generated timing control signal is input from the signal control circuit 119 to the control circuit 113.

Further, in the data comparison portion 110 shown in FIG. 10, the frequency of the input clock signal A-CLK is converted into N times by the PLL circuit 118 and the input clock signal A-CLK with the converted frequency is input to the arithmetic circuit 117. The frequency of the clock signal A-CLK for controlling the driving of the arithmetic circuit 117 may be separately converted by the control circuit 113 and the input clock signal A-CLK with the converted frequency is input to the arithmetic circuit 117. In this case, the frequency of the clock signal for controlling the driving of the arithmetic circuit 117 is controlled by the control circuit 113; thus, the PLL circuit 118 is not necessarily provided.

In the display device of the present invention, data of video signals corresponding to a plurality of line periods or a plurality of frame periods is stored in the RAM 111 and the RAM 112; thus, the data comparison portion 110 can compare data of video signals corresponding to one line period with data of video signals corresponding to other line periods. Accordingly, comparison of not only pieces of data corresponding to adjacent line periods but also pieces of data corresponding to much more line periods can be performed, so that power consumption of the signal line driver circuit 102 can be efficiently suppressed.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 3

In this embodiment mode, a structure of a scan line driver circuit included in a display device of the present invention is described. FIG. 11 shows a block diagram of a structure of the display device of the present invention as an example. FIG. 11 shows a more detailed structure of the scan line driver circuit 101 in the display device shown in FIG. 1. In FIG. 11, the scan line driver circuit 101 includes a shift register 121 and a buffer 122.

The start pulse signal G-SP and the clock signal G-CLK are input to the scan line driver circuit 101. The shift register 103 generates selection signals, pulses of which are sequentially shifted, in accordance with the start pulse signal G-SP and the clock signal G-CLK. The buffer 122 shapes waveforms of the generated selection signal or amplifies the generated selection signal and inputs the signal to the pixel portion 100. The selection signals are input to pixels in each line, and one line can be selected from a plurality of lines by the pulses of the selection signals.

Note that waveform shaping corresponds to controlling the pulse width by a logic circuit using a logic element such as an AND gate, an OR gate, a NAND gate, or a NOR gate. In addition, amplification corresponds to changing amplitude of a signal by using a level shifter, a differential amplifier circuit, or the like, and impedance matching with a wiring in the pixel portion due to size adjustment or the like of a transistor.

A video signal is input from the signal line driver circuit 102 to pixels in the selected line.

The contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 4

In this embodiment mode, a structure of a display device of the present invention is described in which an analog video signal is input to a pixel portion. FIG. 12 shows a diagram of a structure of the display device of the present invention as an example.

The display device of the present invention shown in FIG. 12 includes a pixel portion 200 including a plurality of pixels, a scan line driver circuit 201 which can select a plurality of pixels in each line, and a signal line driver circuit 202 which controls input of a video signal to pixels in a selected line. The signal line driver circuit 202 includes at least a shift register 203, a sampling circuit 204, a plurality of memory circuits, and a digital/analog (D/A) converter circuit 209. FIG. 12 shows an example in which a first latch 205, a second latch 206, a third latch 207, and a fourth latch 208 are used for the plurality of memory circuits. Note that the number of latches used in the display device of the present invention is not limited to four, and the number of latches may be two or three, or may be five or more.

Next, an operation of the signal line driver circuit 202 is described. In the display device shown in FIG. 12, the clock signal S-CLK and the start pulse signal S—SP are input to the shift register 203, similarly to the case of FIG. 1. The shift register 203 generates timing signals, pulses of which are sequentially shifted, in accordance with the clock signal S-CLK and the start pulse signal S—SP and inputs the timing signal to the sampling circuit 204. The sampling circuit 204 samples video signals for one line period, which are input to the signal line driver circuit 202, in accordance with the input timing signal. Then, when all the video signals for one line period are sampled, the sampled video signals are output all at once to one or a plurality of the first latch 205, the second latch 206, the third latch 207, and the fourth latch 208.

Note that in this embodiment mode, an example is described in which all the video signals for one line period are sampled and thereafter, the sampled video signals are input all at once to the memory circuit in the lower stage; however, the present invention is not limited to this structure. A video signal corresponding to each pixel may be sampled and input in each time to the memory circuit in the lower stage without waiting for completion of one line period

In addition, video signals may be sampled sequentially in corresponding pixels, or pixels in one line may be divided into several groups and video signals may be sampled in each pixel corresponding to each group at the same time.

In this embodiment mode, the number of memory elements included in each memory circuit is determined in accordance with the number of bits of a digital video signal to be input. For example, when display is performed with an 8-bit video signal, each of the first latch 205, the second latch 206, the third latch 207, and the fourth latch 208 includes flip-flop circuits which are eight times the number of pixels included in one line.

The writing latch signals WS₁ to WS₄ which control writing of data included in the video signal and the reading latch signals RS₁ to RS₄ which control reading of stored data are input to the first latch 205, the second latch 206, the third latch 207, and the fourth latch 208, respectively. Specifically, the writing latch signal WS₁ and the reading latch signal RS₁ are input to the first latch 205. The writing latch signal WS₂ and the reading latch signal RS₂ are input to the second latch 206. The writing latch signal WS₃ and the reading latch signal RS₃ are input to the third latch 207. The writing latch signal WS₄ and the reading latch signal RS₄ are input to the fourth latch 208.

In accordance with the writing latch signals WS₁ to WS₄, data of video signals for one line period, which are output from the signal line driver circuit 202, are written to and stored in the first latch 205, the second latch 206, the third latch 207, or the fourth latch 208. Further, in accordance with the reading latch signals RS₁ to RS₄, the data stored in the first latch 205, the second latch 206, the third latch 207, or the fourth latch 208 is input to as a video signal to the D/A converter circuit 209. The D/A converter circuit 209 converts the input digital video signal into an analog video signal and inputs the analog video signal to the pixel portion 200.

Note that although the pixel portion 200 is directly connected to the next stage of the D/A converter circuit 209 in FIG. 12, the present invention is not limited to this structure. A circuit which processes the analog video signal output from the D/A converter circuit 209 can be provided in a previous stage of the pixel portion 200. Examples of the circuit which performs signal processing include a buffer which can shape a waveform and a level shifter which can amplify amplitude.

Then, at the same time as inputting a video signal to the pixel portion 200 from the D/A converter circuit 209, the sampling circuit 204 can sample a video signal corresponding to the next line period again. Note that in the present invention, when the same data as the video signal corresponding to the next line period is stored in advance in one of the first latch 205, the second latch 206, the third latch 207, and the fourth latch 208, sampling of the video signal in the sampling circuit 204 can be stopped.

When sampling is stopped, input of pulses of one or both of the clock signal S-CLK and the start pulse signal S—SP to the shift register 203 is stopped, and generation of a pulse of the timing signal in the shift register 203 is stopped. When output of the pulse of the timing signal from the shift register 203 is stopped, the sampling circuit 204 stops sampling of the video signal. Then, in accordance with the reading latch signals RS₁ to RS₄, the same data as the video signal corresponding to the next line period is input as a video signal to the D/A converter circuit 209 from one of the first latch 205, the second latch 206, the third latch 207, and the fourth latch 208. The D/A converter circuit 209 converts the input digital video signal into an analog video signal and inputs the analog video signal to the pixel portion 200.

As shown in this embodiment mode, in the display device of the present invention, a display element included in the pixel of the pixel portion 200 can perform display using an analog video signal.

The contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 5

In this embodiment mode, a pixel structure of a display device is described. In particular, a pixel structure of a liquid crystal display device is described.

A pixel structure in the case where each liquid crystal mode and a transistor are combined is described with reference to cross-sectional views of a pixel.

Note that as the transistor, a thin film transistor (a TFT) or the like including a non-single crystalline semiconductor layer typified by amorphous silicon, polycrystalline silicon, micro crystalline (also referred to as semi-amorphous) silicon, or the like can be used.

As a structure of the transistor, a top-gate structure, a bottom-gate structure, or the like can be used. Note that a channel-etched transistor, a channel-protective transistor, or the like can be used as a bottom-gate transistor.

FIG. 22 is an example of a cross-sectional view of a pixel in the case where a TN mode and a transistor are combined. By applying the pixel structure shown in FIG. 22 to a liquid crystal display device, a liquid crystal display device can be formed at low cost.

Features of the pixel structure shown in FIG. 22 are described. Liquid crystal molecules 10118 shown in FIG. 22 are long and narrow molecules each having a major axis and a minor axis. In FIG. 22, a direction of each of the liquid crystal molecules 10118 is expressed by the length thereof. That is, the direction of the major axis of the liquid crystal molecule 10118, which is expressed as long, is parallel to the page, and as the liquid crystal molecule 10118 is expressed to be shorter, the direction of the major axis becomes closer to a normal direction of the page. That is, among the liquid crystal molecules 10118 shown in FIG. 22, the direction of the major axis of the liquid crystal molecule 10118 which is close to the first substrate 10101 and the direction of the major axis of the liquid crystal molecule 10118 which is close to the second substrate 10116 are different from each other by 90 degrees, and the directions of the major axes of the liquid crystal molecules 10118 located therebetween are arranged so as to link the above two directions smoothly. That is, the liquid crystal molecules 10118 shown in FIG. 22 are aligned to be twisted by 90 degrees between the first substrate 10101 and the second substrate 10116.

Note that the case is described in which a bottom-gate transistor using an amorphous semiconductor is used as the transistor. In the case where a transistor using an amorphous semiconductor is used, a liquid crystal display device can be formed at low cost by using a large substrate.

A liquid crystal display device includes a basic portion displaying images, which is called a liquid crystal panel. The liquid crystal panel is manufactured as follows: two processed substrates are attached to each other with a gap of several μm therebetween, and a liquid crystal material is injected into a space between the two substrates. In FIG. 22, the two substrates correspond to the first substrate 10101 and the second substrate 10116. A transistor and a pixel electrode are formed over the first substrate. A light-shielding film 10114, a color filter 10115, a fourth conductive layer 10113, a spacer 10117, and a second alignment film 10112 are formed on the second substrate.

The light-shielding film 10114 is not necessarily formed on the second substrate 10116. When the light-shielding film 10114 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the light-shielding film 10114 is not formed, yield can be improved. Alternatively, when the light-shielding film 10114 is formed, a display device with little light leakage at the time of black display can be obtained.

The color filter 10115 is not necessarily formed on the second substrate 10116. When the color filter 10115 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the color filter 10115 is not formed, yield can be improved. Note that even when the color filter 10115 is not formed, a display device which can perform color display can be obtained by field sequential driving. Alternatively, when the color filter 10115 is formed, a display device which can perform color display can be obtained.

Spherical spacers may be dispersed on the second substrate 10116 instead of forming the spacer 10117. When the spherical spacers are dispersed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the spherical spacers are dispersed, yield can be improved. Alternatively, when the spacer 10117 is formed, a distance between the two substrates can be uniform because a position of the spacer is not varied, so that a display device with little display unevenness can be obtained.

A process to be performed to the first substrate 10101 is described.

First, a first insulating film 10102 is formed over the first substrate 10101 by sputtering, a printing method, a coating method, or the like. Note that the first insulating film 10102 is not necessarily formed. The first insulating film 10102 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10101 which affects a semiconductor layer.

Next, a first conductive layer 10103 is formed over the first insulating film 10102 by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a second insulating film 10104 is formed over the entire surface by sputtering, a printing method, a coating method, or the like. The second insulating film 10104 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10101 which affects the semiconductor layer.

Next, a first semiconductor layer 10105 and a second semiconductor layer 10106 are formed. Note that the first semiconductor layer 10105 and the second semiconductor layer 10106 are formed sequentially and shapes thereof are processed at the same time.

Next, a second conductive layer 10107 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Note that as a method for etching which is performed at the time of processing a shape of the second conductive layer 10107, dry etching is preferable. Note that either a light-transmitting material or a reflective material may be used for the second conductive layer 10107.

Next, a channel formation region of the transistor is formed. Here, an example of a step thereof is described. The second semiconductor layer 10106 is etched by using the second conductive layer 10107 as a mask. Alternatively, the second semiconductor layer 10106 is etched by using a mask for processing the shape of the second conductive layer 10107. Then, the first conductive layer 10103 at a position where the second semiconductor layer 10106 is removed serves as the channel formation region of the transistor. Thus, the number of masks can be reduced, so that manufacturing cost can be reduced.

Next, a third insulating film 10108 is formed and a contact hole is selectively formed in the third insulating film 10108. Note that a contact hole may be formed also in the second insulating film 10104 at the same time as forming the contact hole in the third insulating film 10108. Note that a surface of the third insulating film 10108 is preferably as even as possible. This is because alignment of the liquid crystal molecules are affected by unevenness of a surface with which the liquid crystal is in contact.

Next, a third conductive layer 10109 is formed by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a first alignment film 10110 is formed. Note that after the first alignment film 10110 is formed, rubbing may be performed so as to control the alignment of the liquid crystal molecules. Rubbing is a step of forming stripes on an alignment film by rubbing the alignment film with a cloth. By performing rubbing, the alignment film can have alignment properties.

The first substrate 10101 which is manufactured as described above and the second substrate 10116 on which the light-shielding film 10114, the color filter 10115, the fourth conductive layer 10113, the spacer 10117, and the second alignment film 10112 are formed are attached to each other by a sealant with a gap of several μm therebetween. Then, a liquid crystal material is injected into a space between the two substrates. Note that in the TN mode, the fourth conductive layer 10113 is formed over the entire surface of the second substrate 10116.

FIG. 23A is an example of a cross-sectional view of a pixel in the case where an MVA (multi-domain vertical alignment) mode and a transistor are combined. By applying the pixel structure shown in FIG. 23A to a liquid crystal display device, a liquid crystal display device having a wide viewing angle, high response speed, and high contrast can be obtained.

Features of the pixel structure shown in FIG. 23A are described. Liquid crystal molecules 10218 shown in FIG. 23A are long and narrow molecules each having a major axis and a minor axis. In FIG. 23A, a direction of each of the liquid crystal molecules 10218 is expressed by the length thereof. That is, the direction of the major axis of the liquid crystal molecule 10218, which is expressed as long, is parallel to the page, and as the liquid crystal molecule 10218 is expressed to be shorter, the direction of the major axis becomes closer to a normal direction of the page. That is, each of the liquid crystal molecules 10218 shown in FIG. 23A is aligned such that the direction of the major axis is normal to the alignment film. Thus, the liquid crystal molecules 10218 at a position where an alignment control protrusion 10219 is formed are aligned radially with the alignment control protrusion 10219 as a center. With this state, a liquid crystal display device having a wide viewing angle can be obtained.

Note that the case is described in which a bottom-gate transistor using an amorphous semiconductor is used as the transistor. In the case where a transistor using an amorphous semiconductor is used, a liquid crystal display device can be formed at low cost by using a large substrate.

A liquid crystal display device includes a basic portion displaying images, which is called a liquid crystal panel. The liquid crystal panel is manufactured as follows: two processed substrates are attached to each other with a gap of several μm therebetween, and a liquid crystal material is injected into a space between the two substrates. In FIG. 23A, the two substrates correspond to the first substrate 10201 and the second substrate 10216. A transistor and a pixel electrode are formed over the first substrate. A light-shielding film 10214, a color filter 10215, a fourth conductive layer 10213, a spacer 10217, a second alignment film 10212, and an alignment control protrusion 10219 are formed on the second substrate.

The light-shielding film 10214 is not necessarily formed on the second substrate 10216. When the light-shielding film 10214 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the light-shielding film 10214 is not formed, yield can be improved. Alternatively, when the light-shielding film 10214 is formed, a display device with little light leakage at the time of black display can be obtained.

The color filter 10215 is not necessarily formed on the second substrate 10216. When the color filter 10215 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the color filter 10215 is not formed, yield can be improved. Note that even when the color filter 10215 is not formed, a display device which can perform color display can be obtained by field sequential driving. Alternatively, when the color filter 10215 is formed, a display device which can perform color display can be obtained.

Spherical spacers may be dispersed on the second substrate 10216 instead of forming the spacer 10217. When the spherical spacers are dispersed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the spherical spacers are dispersed, yield can be improved. Alternatively, when the spacer 10217 is formed, a distance between the two substrates can be uniform because a position of the spacer is not varied, so that a display device with little display unevenness can be obtained.

A process to be performed to the first substrate 10201 is described.

First, a first insulating film 10202 is formed over the first substrate 10201 by sputtering, a printing method, a coating method, or the like. Note that the first insulating film 10202 is not necessarily formed. The first insulating film 10202 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10201 which affects a semiconductor layer.

Next, a first conductive layer 10203 is formed over the first insulating film 10202 by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a second insulating film 10204 is formed over the entire surface by sputtering, a printing method, a coating method, or the like. The second insulating film 10204 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10201 which affects the semiconductor layer.

Next, a first semiconductor layer 10205 and a second semiconductor layer 10206 are formed. Note that the first semiconductor layer 10205 and the second semiconductor layer 10206 are formed sequentially and shapes thereof are processed at the same time.

Next, a second conductive layer 10207 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Note that as a method for etching which is performed at the time of processing a shape of the second conductive layer 10207, dry etching is preferable. Note that as the second conductive layer 10207, either a light-transmitting material or a reflective material may be used.

Next, a channel formation region of the transistor is formed. Here, an example of a step thereof is described. The second semiconductor layer 10206 is etched by using the second conductive layer 10207 as a mask. Alternatively, the second semiconductor layer 10206 is etched by using a mask for processing the shape of the second conductive layer 10207. Then, the first conductive layer 10203 at a position where the second semiconductor layer 10206 is removed serves as the channel formation region of the transistor. Thus, the number of masks can be reduced, so that manufacturing cost can be reduced.

Next, a third insulating film 10208 is formed and a contact hole is selectively formed in the third insulating film 10208. Note that a contact hole may be formed also in the second insulating film 10204 at the same time as forming the contact hole in the third insulating film 10208.

Next, a third conductive layer 10209 is formed by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a first alignment film 10210 is formed. Note that after the first alignment film 10210 is formed, rubbing may be performed so as to control the alignment of the liquid crystal molecules. Rubbing is a step of forming stripes on an alignment film by rubbing the alignment film with a cloth. By performing rubbing, the alignment film can have alignment properties.

The first substrate 10201 which is manufactured as described above and the second substrate 10216 on which the light-shielding film 10214, the color filter 10215, the fourth conductive layer 10213, the spacer 10217, and the second alignment film 10212 are manufactured are attached to each other by a sealant with a gap of several μm therebetween. Then, a liquid crystal material is injected into a space between the two substrates. Note that in the MVA mode, the fourth conductive layer 10213 is formed over the entire surface of the second substrate 10216. Note that the alignment control protrusion 10219 is formed so as to be in contact with the fourth conductive layer 10213. The alignment control protrusion 10219 preferably has a shape with a smooth curved surface. Thus, alignment of the adjacent liquid crystal molecules 10218 is extremely similar, so that an alignment defect can be reduced. Further, a defect of the alignment film caused by breaking of the alignment film can be reduced.

FIG. 23B is an example of a cross-sectional view of a pixel in the case where a PVA (patterned vertical alignment) mode and a transistor are combined. By applying the pixel structure shown in FIG. 23B to a liquid crystal display device, a liquid crystal display device having a wide viewing angle, high response speed, and high contrast can be obtained.

Features of the pixel structure shown in FIG. 23B are described. Liquid crystal molecules 10248 shown in FIG. 23B are long and narrow molecules each having a major axis and a minor axis. In FIG. 23B, direction of each of the liquid crystal molecules 10248 is expressed by the length thereof. That is, the direction of the major axis of the liquid crystal molecule 10248, which is expressed as long, is parallel to the page, and as the liquid crystal molecule 10248 is expressed to be shorter, the direction of the major axis becomes closer to a normal direction of the page. That is, each of the liquid crystal molecules 10248 shown in FIG. 23B is aligned such that the direction of the major axis is normal to the alignment film. Thus, the liquid crystal molecules 10248 at a position where an electrode notch portion 10249 is formed are aligned radially with a boundary of the electrode notch portion 10249 and the fourth conductive layer 10243 as a center. With this state, a liquid crystal display device having a wide viewing angle can be obtained.

Note that the case is described in which a bottom-gate transistor using an amorphous semiconductor is used as the transistor. In the case where a transistor using an amorphous semiconductor is used, a liquid crystal display device can be formed at low cost by using a large substrate.

A liquid crystal display device includes a basic portion displaying images, which is called a liquid crystal panel. The liquid crystal panel is manufactured as follows: two processed substrates are attached to each other with a gap of several μm therebetween, and a liquid crystal material is injected into a space between the two substrates. In FIG. 23B, the two substrates correspond to the first substrate 10231 and the second substrate 10246. A transistor and a pixel electrode are formed over the first substrate. A light-shielding film 10244, a color filter 10245, a fourth conductive layer 10243, a spacer 10247, and a second alignment film 10242 are formed on the second substrate.

The light-shielding film 10244 is not necessarily formed on the second substrate 10246. When the light-shielding film 10244 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the light-shielding film 10244 is not formed, yield can be improved. Alternatively, when the light-shielding film 10244 is formed, a display device with little light leakage at the time of black display can be obtained.

The color filter 10245 is not necessarily formed on the second substrate 10246. When the color filter 10245 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the color filter 10245 is not formed, yield can be improved. Note that even when the color filter 10245 is not formed, a display device which can perform color display can be obtained by field sequential driving. Alternatively, when the color filter 10245 is formed, a display device which can perform color display can be obtained.

Spherical spacers may be dispersed on the second substrate 10246 instead of forming the spacer 10247. When the spherical spacers are dispersed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the spherical spacers are dispersed, yield can be improved. Alternatively, when the spacer 10247 is formed, a distance between the two substrates can be uniform because a position of the spacer is not varied, so that a display device with little display unevenness can be obtained.

A process to be performed to the first substrate 10231 is described.

First, a first insulating film 10232 is formed over the first substrate 10231 by sputtering, a printing method, a coating method, or the like. Note that the first insulating film 10232 is not necessarily formed. The first insulating film 10232 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10231 which affects a semiconductor layer.

Next, a first conductive layer 10233 is formed over the first insulating film 10232 by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a second insulating film 10234 is formed over the entire surface by sputtering, a printing method, a coating method, or the like. The second insulating film 10234 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10231 which affects the semiconductor layer.

Next, a first semiconductor layer 10235 and a second semiconductor layer 10236 are formed. Note that the first semiconductor layer 10235 and the second semiconductor layer 10236 are formed sequentially and shapes thereof are processed at the same time.

Next, a second conductive layer 10237 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Note that as a method for etching which is performed at the time of processing a shape of the second conductive layer 10237, dry etching is preferable. Note that as the second conductive layer 10237, either a light-transmitting material or a reflective material may be used.

Next, a channel formation region of the transistor is formed. Here, an example of a step thereof is described. The second semiconductor layer 10236 is etched by using the second conductive layer 10237 as a mask. Alternatively, the second semiconductor layer 10236 is etched by using a mask for processing the shape of the second conductive layer 10107. Then, the first conductive layer 10233 at a position where the second semiconductor layer 10236 is removed serves as the channel formation region of the transistor. Thus, the number of masks can be reduced, so that manufacturing cost can be reduced.

Next, a third insulating film 10238 is formed and a contact hole is selectively formed in the third insulating film 10238. Note that a contact hole may be formed also in the second insulating film 10234 at the same time as forming the contact hole in the third insulating film 10238. Note that a surface of the third insulating film 10238 is preferably as even as possible. This is because alignment of the liquid crystal molecules are affected by unevenness of a surface with which the liquid crystal is in contact.

Next, a third conductive layer 10239 is formed by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a first alignment film 10240 is formed. Note that after the first alignment film 10240 is formed, rubbing may be performed so as to control the alignment of the liquid crystal molecules. Rubbing is a step of forming stripes on an alignment film by rubbing the alignment film with a cloth. By performing rubbing, the alignment film can have alignment properties.

The first substrate 10231 which is manufactured as described above and the second substrate 10246 on which the light-shielding film 10244, the color filter 10245, the fourth conductive layer 10243, the spacer 10247, and the second alignment film 10242 are manufactured are attached to each other by a sealant with a gap of several μm therebetween. Then, a liquid crystal material is injected into a space between the two substrates. Note that in the PVA mode, the fourth conductive layer 10243 is patterned and is provided with the electrode notch portion 10249. Although a shape of the electrode notch portion 10249 is not particularly limited, the electrode notch portion 10249 preferably has a shape in which a plurality of rectangles having different directions are combined. Thus, a plurality of regions having different alignment can be formed, so that a liquid crystal display device having a wide viewing angle can be obtained. Note that the fourth conductive layer 10243 at the boundary between the electrode notch portion 10249 and the fourth conductive layer 10243 preferably has a shape with a smooth curved surface. Thus, alignment of the adjacent liquid crystal molecules 10248 is extremely similar, so that an alignment defect is reduced. Further, a defect of the alignment film caused by breaking of the second alignment film 10242 by the electrode notch portion 10249 can be prevented.

FIG. 24A is an example of a cross-sectional view of a pixel in the case where an IPS (in-plane-switching) mode and a transistor are combined. By applying the pixel structure shown in FIG. 24A to a liquid crystal display device, a liquid crystal display device theoretically having a wide viewing angle and response speed which has low dependency on a gray scale can be obtained.

Features of the pixel structure shown in FIG. 24A are described. Liquid crystal molecules 10318 shown in FIG. 24A are long and narrow molecules each having a major axis and a minor axis. In FIG. 24A, a direction of each of the liquid crystal molecules 10318 is expressed by the length thereof. That is, the direction of the major axis of the liquid crystal molecule 10318, which is expressed as long, is parallel to the page, and as the liquid crystal molecule 10318 is expressed to be shorter, the direction of the major axis becomes closer to a normal direction of the page. That is, each of the liquid crystal molecules 10318 shown in FIG. 24A is aligned so that the direction of the major axis thereof is always horizontal to the substrate. Although FIG. 24A shows alignment with no electric field, when an electric field is applied to each of the liquid crystal molecules 10318, each of the liquid crystal molecules 10318 rotates in a horizontal plane as the direction of the major axis thereof is always horizontal to the substrate. With this state, a liquid crystal display device having a wide viewing angle can be obtained.

Note that the case is described in which a bottom-gate transistor using an amorphous semiconductor is used as the transistor. In the case where a transistor using an amorphous semiconductor is used, a liquid crystal display device can be formed at low cost by using a large substrate.

A liquid crystal display device includes a basic portion displaying images, which is called a liquid crystal panel. The liquid crystal panel is manufactured as follows: two processed substrates are attached to each other with a gap of several μm therebetween, and a liquid crystal material is injected into a space between the two substrates. In FIG. 24A, the two substrates correspond to the first substrate 10301 and the second substrate 10316. A transistor and a pixel electrode are formed over the first substrate. A light-shielding film 10314, a color filter 10315, a fourth conductive layer 10313, a spacer 10317, and a second alignment film 10312 are formed on the second substrate.

The light-shielding film 10314 is not necessarily formed on the second substrate 10316. When the light-shielding film 10314 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the light-shielding film 10314 is not formed, yield can be improved. Alternatively, when the light-shielding film 10314 is formed, a display device with little light leakage at the time of black display can be obtained.

The color filter 10315 is not necessarily formed on the second substrate 10316. When the color filter 10315 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the color filter 10315 is not formed, yield can be improved. Note that even when the color filter 10315 is not formed, a display device which can perform color display can be obtained by field sequential driving. Alternatively, when the color filter 10315 is formed, a display device which can perform color display can be obtained.

Spherical spacers may be dispersed on the second substrate 10316 instead of forming the spacer 10317. When the spherical spacers are dispersed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the spherical spacers are dispersed, yield can be improved. Alternatively, when the spacer 10317 is formed, a distance between the two substrates can be uniform because a position of the spacer is not varied, so that a display device with little display unevenness can be obtained.

A process to be performed to the first substrate 10301 is described.

First, a first insulating film 10302 is formed over the first substrate 10301 by sputtering, a printing method, a coating method, or the like. Note that the first insulating film 10302 is not necessarily formed. The first insulating film 10302 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10301 which affects a semiconductor layer.

Next, a first conductive layer 10303 is formed over the first insulating film 10302 by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a second insulating film 10304 is formed over the entire surface by sputtering, a printing method, a coating method, or the like. The second insulating film 10304 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10301 which affects the semiconductor layer.

Next, a first semiconductor layer 10305 and a second semiconductor layer 10306 are formed. Note that the first semiconductor layer 10305 and the second semiconductor layer 10306 are formed sequentially and shapes thereof are processed at the same time.

Next, a second conductive layer 10307 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Note that as a method for etching which is performed at the time of processing a shape of the second conductive layer 10307, dry etching is preferable. Note that as the second conductive layer 10307, either a light-transmitting material or a reflective material may be used.

Next, a channel formation region of the transistor is formed. Here, an example of a step thereof is described. The second semiconductor layer 10106 is etched by using the second conductive layer 10307 as a mask. Alternatively, the second semiconductor layer 10306 is etched by using a mask for processing the shape of the second conductive layer 10307. Then, the first conductive layer 10303 at a position where the second semiconductor layer 10306 is removed serves as the channel formation region of the transistor. Thus, the number of masks can be reduced, so that manufacturing cost can be reduced.

Next, a third insulating film 10308 is formed and a contact hole is selectively formed in the third insulating film 10308. Note that a contact hole may be formed also in the second insulating film 10304 at the same time as forming the contact hole in the third insulating film 10308.

Next, a third conductive layer 10309 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Here, the third conductive layer 10309 has a shape in which two comb-shaped electrodes engage with each other. One of the comb-shaped electrodes is electrically connected to one of a source electrode and a drain electrode of the transistor, and the other of the comb-shaped electrodes is electrically connected to a common electrode. Thus, a horizontal electric field can be effectively applied to the liquid crystal molecules 10318.

Next, a first alignment film 10310 is formed. Note that after the first alignment film 10310 is formed, rubbing may be performed so as to control the alignment of the liquid crystal molecules. Rubbing is a step of forming stripes on an alignment film by rubbing the alignment film with a cloth. By performing rubbing, the alignment film can have alignment properties.

The first substrate 10301 which is manufactured as described above and the second substrate 10316 on which the light-shielding film 10314, the color filter 10315, the spacer 10317, and the second alignment film 10312 are formed are attached to each other by a sealant with a gap of several μm therebetween. Then, a liquid crystal material is injected into a space between the two substrates.

FIG. 24B is an example of a cross-sectional view of a pixel in the case where an FFS (fringe field switching) mode and a transistor are combined. By applying the pixel structure shown in FIG. 24B to a liquid crystal display device, a liquid crystal display device theoretically having a wide viewing angle and response speed which has low dependency on a gray scale can be obtained.

Features of the pixel structure shown in FIG. 24B are described. Liquid crystal molecules 10348 shown in FIG. 24B are long and narrow molecules each having a major axis and a minor axis. In FIG. 24B, direction of each of the liquid crystal molecules 10348 is expressed by the length thereof. That is, the direction of the major axis of the liquid crystal molecule 10348, which is expressed as long, is parallel to the page, and as the liquid crystal molecule 10348 is expressed to be shorter, the direction of the major axis becomes closer to a normal direction of the page. That is, each of the liquid crystal molecules 10348 shown in FIG. 24B is aligned so that the direction of the major axis thereof is always horizontal to the substrate. Although FIG. 24B shows alignment with no electric field, when an electric field is applied to each of the liquid crystal molecules 10348, each of the liquid crystal molecules 10348 rotates in a horizontal plane as the direction of the major axis thereof is always horizontal to the substrate. With this state, a liquid crystal display device having a wide viewing angle can be obtained.

Note that the case is described in which a bottom-gate transistor using an amorphous semiconductor is used as the transistor. In the case where a transistor using an amorphous semiconductor is used, a liquid crystal display device can be formed at low cost by using a large substrate.

A liquid crystal display device includes a basic portion displaying images, which is called a liquid crystal panel. The liquid crystal panel is manufactured as follows: two processed substrates are attached to each other with a gap of several μm therebetween, and a liquid crystal material is injected into a space between the two substrates. In FIG. 24B, the two substrates correspond to the first substrate 10331 and the second substrate 10346. A transistor and a pixel electrode are formed over the first substrate. A light-shielding film 10344, a color filter 10345, a fourth conductive layer 10343, a spacer 10347, and a second alignment film 10342 are formed on the second substrate.

The light-shielding film 10344 is not necessarily formed on the second substrate 10346. When the light-shielding film 10344 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the light-shielding film 10344 is not formed, yield can be improved. Alternatively, when the light-shielding film 10344 is formed, a display device with little light leakage at the time of black display can be obtained.

The color filter 10345 is not necessarily formed on the second substrate 10346. When the color filter 10345 is not formed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the color filter 10345 is not formed, yield can be improved. Note that even when the color filter 10345 is not formed, a display device which can perform color display can be obtained by field sequential driving. Alternatively, when the color filter 10345 is formed, a display device which can perform color display can be obtained.

Spherical spacers may be dispersed on the second substrate 10346 instead of forming the spacer 10347. When the spherical spacers are dispersed, the number of steps is reduced, so that manufacturing cost can be reduced. In addition, since a structure is simple when the spherical spacers are dispersed, yield can be improved. Alternatively, when the spacer 10347 is formed, a distance between the two substrates can be uniform because a position of the spacer is not varied, so that a display device with little display unevenness can be obtained.

A process to be performed to the first substrate 10331 is described.

First, a first insulating film 10332 is formed over the first substrate 10331 by sputtering, a printing method, a coating method, or the like. Note that the first insulating film 10332 is not necessarily formed. The first insulating film 10332 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10331 which affects a semiconductor layer.

Next, a first conductive layer 10333 is formed over the first insulating film 10332 by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a second insulating film 10334 is formed over the entire surface by sputtering, a printing method, a coating method, or the like. The second insulating film 10334 has a function of preventing change in characteristics of the transistor due to an impurity from the first substrate 10331 which affects the semiconductor layer.

Next, a first semiconductor layer 10335 and a second semiconductor layer 10336 are formed. Note that the first semiconductor layer 10335 and the second semiconductor layer 10336 are formed sequentially and shapes thereof are processed at the same time.

Next, a second conductive layer 10337 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Note that as a method for etching which is performed at the time of processing a shape of the second conductive layer 10337, dry etching is preferable. Note that as the second conductive layer 10337, either a light-transmitting material or a reflective material may be used.

Next, a channel formation region of the transistor is formed. Here, an example of a step thereof is described. The second semiconductor layer 10106 is etched by using the second conductive layer 10337 as a mask. Alternatively, the second semiconductor layer 10336 is etched by using a mask for processing the shape of the second conductive layer 10337. Then, the first conductive layer 10333 at a position where the second semiconductor layer 10336 is removed serves as the channel formation region of the transistor. Thus, the number of masks can be reduced, so that manufacturing cost can be reduced.

Next, a third insulating film 10338 is formed and a contact hole is selectively formed in the third insulating film 10338.

Next, a fourth conductive layer 10343 is formed by photolithography, a laser direct writing method, an inkjet method, or the like.

Next, a fourth insulating film 10349 is formed and a contact hole is selectively formed in the fourth insulating film 10349. Note that a surface of the fourth insulating film 10349 is preferably as even as possible. This is because alignment of the liquid crystal molecules are affected by unevenness of a surface with which the liquid crystal is in contact.

Next, a third conductive layer 10339 is formed by photolithography, a laser direct writing method, an inkjet method, or the like. Here, the third conductive layer 10339 is comb-shaped.

Next, a first alignment film 10340 is formed. Note that after the first alignment film 10340 is formed, rubbing may be performed so as to control the alignment of the liquid crystal molecules. Rubbing is a step of forming stripes on an alignment film by rubbing the alignment film with a cloth. By performing rubbing, the alignment film can have alignment properties.

The first substrate 10331 which is manufactured as described above and the second substrate 10346 on which the light-shielding film 10344, the color filter 10345, the spacer 10347, and the second alignment film 10342 are formed are attached to each other by a sealant with a gap of several μm therebetween. Then, a liquid crystal material is injected into a space between the two substrates. Therefore, a liquid crystal panel can be manufactured.

Here, materials which can be used for conductive layers or insulating films are described.

As the first insulating film 10102 in FIG. 22, the first insulating film 10202 in FIG. 23A, the first insulating film 10232 in FIG. 23B, the first insulating film 10302 in FIG. 24A, or the first insulating film 10332 in FIG. 24B, an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride (SiO_(x)N_(y)) film can be used. Alternatively, an insulating film having a stacked-layer structure in which two or more of a silicon oxide film, a silicon nitride film, a silicon oxynitride (SiO_(x)N_(y)) film, and the like are combined can be used as.

As the first conductive layer 10103 in FIG. 22, the first conductive layer 10203 in FIG. 23A, the first conductive layer 10233 in FIG. 23B, the first conductive layer 10303 in FIG. 24A, or the first conductive layer 10333 in FIG. 24B, Mo, Ti, Al, Nd, Cr, or the like can be used. Alternatively, a stacked-layer structure in which two or more of Mo, Ti, Al, Nd, Cr, and the like are combined can be used.

As the second insulating film 10104 in FIG. 22, the second insulating film 10204 in FIG. 23A, the second insulating film 10234 in FIG. 23B, the second insulating film 10304 in FIG. 24A, or the second insulating film 10334 in FIG. 24B, a thermal oxide film, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or the like can be used. Alternatively, a stacked-layer structure in which two or more of a thermal oxide film, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, and the like are combined can be used. Note that a silicon oxide film is preferable in a portion which is in contact with a semiconductor layer. This is because a trap level at an interface with the semiconductor layer decreases when a silicon oxide film is used. Note that a silicon nitride film is preferable in a portion which is in contact with Mo. This is because a silicon nitride film does not oxidize Mo.

As the first semiconductor layer 10105 in FIG. 22, the first semiconductor layer 10205 in FIG. 23A, the first semiconductor layer 10235 in FIG. 23B, the first semiconductor layer 10305 in FIG. 24A, or the first semiconductor layer 10335 in FIG. 24B, silicon, silicon germanium (SiGe), or the like can be used.

As the second semiconductor layer 10106 in FIG. 22, the second semiconductor layer 10206 in FIG. 23A, the second semiconductor layer 10236 in FIG. 23B, the second semiconductor layer 10306 in FIG. 24A, or the second semiconductor layer 10336 in FIG. 24B, silicon or the like including phosphorus can be used, for example.

As a light-transmitting material of the second conductive layer 10107 and the third conductive layer 10109 in FIG. 22; the second conductive layer 10207 and the third conductive layer 10209 in FIG. 23A; the second conductive layer 10237 and the third conductive layer 10239 in FIG. 23B; the second conductive layer 10307 and the third conductive layer 10309 in FIG. 24A; or the second conductive layer 10337, the third conductive layer 10339, and a fourth conductive layer 10343 in FIG. 24B, an indium tin oxide (ITO) film formed by mixing tin oxide into indium oxide, an indium tin silicon oxide (ITSO) film formed by mixing silicon oxide into indium tin oxide (ITO), an indium zinc oxide (IZO) film formed by mixing zinc oxide into indium oxide, a zinc oxide film, a tin oxide film, or the like can be used. Note that IZO is a light-transmitting conductive material formed by sputtering using a target in which zinc oxide (ZnO) is mixed into ITO at 2 to 20 wt %.

As a reflective material of the second conductive layer 10107 and the third conductive layer 10109 in FIG. 22; the second conductive layer 10207 and the third conductive layer 10209 in FIG. 23A; the second conductive layer 10237 and the third conductive layer 10239 in FIG. 23B; the second conductive layer 10307 and the third conductive layer 10309 in FIG. 24A; or the second conductive layer 10337, the third conductive layer 10339, and the fourth conductive layer 10343 in FIG. 24B, Ti, Mo, Ta, Cr, W, Al, or the like can be used. Alternatively, a two-layer structure in which Al and Ti, Mo, Ta, Cr, or W are stacked, or a three-layer structure in which Al is interposed between metals such as Ti, Mo, Ta, Cr, and W may be used.

As the third insulating film 10108 in FIG. 22, the third insulating film 10208 in FIG. 23A, the third insulating film 10238 in FIG. 23B, the third conductive layer 10239 in FIG. 23B, the third insulating film 10308 in FIG. 24A, or the third insulating film 10338 and the fourth insulating film 10349 in FIG. 24B, an inorganic material (e.g., silicon oxide, silicon nitride, or silicon oxynitride), an organic compound material having a low dielectric constant (e.g., a photosensitive or nonphotosensitive organic resin material), or the like can be used. Alternatively, a material including siloxane can be used. Note that siloxane is a material in which a skeleton structure is formed by a bond of silicon (Si) and oxygen (O). As a substituent, an organic group including at least hydrogen (e.g., an alkyl group or aromatic hydrocarbon) is used. Alternatively, a fluoro group may be used as the substituent. Further alternatively, the organic group including at least hydrogen and the fluoro group may be used as the substituent.

As the first alignment film 10110 in FIG. 22, the first alignment film 10210 in FIG. 23A, the first alignment film 10240 in FIG. 23B, the first alignment film 10310 in FIG. 24A, or the first alignment film 10340 in FIG. 24B, a film of a high molecular compound such as polyimide can be used.

Next, the pixel structure in the case where each liquid crystal mode and the transistor are combined is described with reference to a top plan view (a layout diagram) of the pixel.

Note that as a liquid crystal mode, a TN (twisted nematic) mode, an IPS (in-plane-switching) mode, an FFS (fringe field switching) mode, an MVA (multi-domain vertical alignment) mode, a PVA (patterned vertical alignment) mode, an ASM (axially symmetric aligned micro-cell) mode, an OCB (optical compensated birefringence) mode, an FLC (ferroelectric liquid crystal) mode, an AFLC (antiferroelectric liquid crystal) mode, or the like can be used.

As the transistor, a thin film transistor (a TFT) including a non-single crystalline semiconductor layer typified by amorphous silicon, polycrystalline silicon, microcrystalline (also referred to as semi-amorphous) silicon, or the like can be used.

Note that as a structure of the transistor, a top-gate structure, a bottom-gate structure, or the like can be used. A channel-etched transistor, a channel-protective transistor, or the like can be used as a bottom-gate transistor.

FIG. 25 is an example of a top plan view of a pixel in the case where a TN mode and a transistor are combined. By applying the pixel structure shown in FIG. 25 to a liquid crystal display device, a liquid crystal display device can be formed at low cost.

The pixel shown in FIG. 25 includes a scan line 10401, an image signal line 10402, a capacitor line 10403, a transistor 10404, a pixel electrode 10405, and a pixel capacitor 10406.

The scan line 10401 has a function of transmitting a signal (a scan signal) to the pixel. The image signal line 10402 has a function for transmitting a signal (an image signal) to the pixel. Note that since the scan line 10401 and the image signal line 10402 are arranged in matrix, they are formed of conductive layers in different layers. Note that a semiconductor layer may be provided at an intersection of the scan line 10401 and the image signal line 10402. Thus, intersection capacitance formed between the scan line 10401 and the image signal line 10402 can be reduced.

The capacitor line 10403 is provided in parallel to the pixel electrode 10405. A portion where the capacitor line 10403 and the pixel electrode 10405 overlap with each other corresponds to the pixel capacitor 10406. Note that part of the capacitor line 10403 is extended along the image signal line 10402 so as to surround the image signal line 10402. Thus, crosstalk can be reduced. Crosstalk is a phenomenon in which a potential of an electrode, which should hold the potential, is changed in accordance with change in potential of the image signal line 10402. Note that intersection capacitance can be reduced by providing a semiconductor layer between the capacitor line 10403 and the image signal line 10402. Note that the capacitor line 10403 is formed of a material which is similar to that of the scan line 10401.

The transistor 10404 has a function as a switch which turns on the image signal line 10402 and the pixel electrode 10405. Note that one of a source region and a drain region of the transistor 10404 is provided so as to be surrounded by the other of the source region and the drain region of the transistor 10404. Thus, the channel width of the transistor 10404 increases, so that switching capability can be improved. Note that a gate electrode of the transistor 10404 is provided so as to surround the semiconductor layer.

The pixel electrode 10405 is electrically connected to one of a source electrode and a drain electrode of the transistor 10404. The pixel electrode 10405 is an electrode for applying signal voltage which is transmitted by the image signal line 10402 to a liquid crystal element. Note that the pixel electrode 10405 is rectangular. Thus, an aperture ratio can be improved. Note that as the pixel electrode 10405, a light-transmitting material or a reflective material may be used. Alternatively, the pixel electrode 10405 may be formed by combining a light-transmitting material and a reflective material.

FIG. 26A is an example of a top plan view of a pixel in the case where an MVA mode and a transistor are combined. By applying the pixel structure shown in FIG. 26A to a liquid crystal display device, a liquid crystal display device having a wide viewing angle, high response speed, and high contrast can be obtained.

The pixel shown in FIG. 26A includes a scan line 10501, a video signal line 10502, a capacitor line 10503, a transistor 10504, a pixel electrode 10505, a pixel capacitor 10506, and an alignment control protrusion 10507.

The scan line 10501 has a function of transmitting a signal (a scan signal) to the pixel. The image signal line 10502 has a function for transmitting a signal (an image signal) to the pixel. Note that since the scan line 10501 and the image signal line 10502 are arranged in matrix, they are formed of conductive layers in different layers. Note that a semiconductor layer may be provided at an intersection of the scan line 10501 and the image signal line 10502. Thus, intersection capacitance formed between the scan line 10501 and the image signal line 10502 can be reduced.

The capacitor line 10503 is provided in parallel to the pixel electrode 10505. A portion where the capacitor line 10503 and the pixel electrode 10505 overlap with each other corresponds to the pixel capacitor 10506. Note that part of the capacitor line 10503 is extended along the image signal line 10502 so as to surround the image signal line 10502. Thus, crosstalk can be reduced. Crosstalk is a phenomenon in which a potential of an electrode, which should hold the potential, is changed in accordance with change in potential of the image signal line 10502. Note that intersection capacitance can be reduced by providing a semiconductor layer between the capacitor line 10503 and the image signal line 10502. Note that the capacitor line 10503 is formed of a material which is similar to that of the scan line 10501.

The transistor 10504 has a function as a switch which turns on the image signal line 10502 and the pixel electrode 10505. Note that one of a source region and a drain region of the transistor 10504 is provided so as to be surrounded by the other of the source region and the drain region of the transistor 10504. Thus, the channel width of the transistor 10504 increases, so that switching capability can be improved. Note that a gate electrode of the transistor 10504 is provided so as to surround the semiconductor layer.

The pixel electrode 10505 is electrically connected to one of a source electrode and a drain electrode of the transistor 10504. The pixel electrode 10505 is an electrode for applying signal voltage which is transmitted by the image signal line 10502 to a liquid crystal element. Note that the pixel electrode 10505 is rectangular. Thus, an aperture ratio can be improved. Note that as the pixel electrode 10505, a light-transmitting material or a reflective material may be used. Alternatively, the pixel electrode 10505 may be formed by combining a light-transmitting material and a reflective material.

The alignment control protrusion 10507 is formed on a counter substrate. The alignment control protrusion 10507 has a function of aligning liquid crystal molecules radially. Note that a shape of the alignment control protrusion 10507 is not particularly limited. For example, the alignment control protrusion 10507 may be a dogleg shape. Thus, a plurality of regions having different alignment of the liquid crystal molecules can be formed, so that a viewing angle can be improved.

FIG. 26B is an example of a top plan view of a pixel in the case where a PVA mode and a transistor are combined. By applying the pixel structure shown in FIG. 26B to a liquid crystal display device, a liquid crystal display device having a wide viewing angle, high response speed, and high contrast can be obtained.

The pixel shown in FIG. 26B includes a scan line 10511, a video signal line 10512, a capacitor line 10513, a transistor 10514, a pixel electrode 10515, a pixel capacitor 10516, and an electrode notch portion 10517.

The scan line 10511 has a function of transmitting a signal (a scan signal) to the pixel. The image signal line 10512 has a function for transmitting a signal (an image signal) to the pixel. Note that since the scan line 10511 and the image signal line 10512 are arranged in matrix, they are formed of conductive layers in different layers. Note that a semiconductor layer may be provided at an intersection of the scan line 10511 and the image signal line 10512. Thus, intersection capacitance formed between the scan line 10511 and the image signal line 10512 can be reduced.

The capacitor line 10513 is provided in parallel to the pixel electrode 10515. A portion where the capacitor line 10513 and the pixel electrode overlap with each other corresponds to the pixel capacitor 10516. Note that part of the capacitor line 10513 is extended along the image signal line 10512 so as to surround the image signal line 10512. Thus, crosstalk can be reduced. Crosstalk is a phenomenon in which a potential of an electrode, which should hold the potential, is changed in accordance with change in potential of the image signal line 10512. Note that intersection capacitance can be reduced by providing a semiconductor layer between the capacitor line 10513 and the image signal line 10512. Note that the capacitor line 10513 is formed of a material which is similar to that of the scan line 10511.

The transistor 10514 has a function as a switch which turns on the image signal line 10512 and the pixel electrode 10515. Note that one of a source region and a drain region of the transistor 10514 is provided so as to be surrounded by the other of the source region and the drain region of the transistor 10514. Thus, the channel width of the transistor 10514 increases, so that switching capability can be improved. Note that a gate electrode of the transistor 10514 is provided so as to surround the semiconductor layer.

The pixel electrode 10515 is electrically connected to one of a source electrode and a drain electrode of the transistor 10514. The pixel electrode 10515 is an electrode for applying signal voltage which is transmitted by the image signal line 10512 to a liquid crystal element. Note that the pixel electrode 10515 has a shape which is formed in accordance with a shape of the electrode notch portion 10517. Specifically, the pixel electrode 10515 has a shape in which a portion where the pixel electrode 10515 is notched is formed in a portion where the electrode notch portion 10517 is not formed. Thus, a plurality of regions having different alignment of the liquid crystal molecules can be formed, so that a viewing angle can be improved. Note that as the pixel electrode 10515, a light-transmitting material or a reflective material may be used. Alternatively, the pixel electrode 10515 may be formed by combining a light-transmitting material and a reflective material.

FIG. 27A is an example of a top plan view of a pixel in the case where an IPS mode and a transistor are combined. By applying the pixel structure shown in FIG. 27A to a liquid crystal display device, a liquid crystal display device theoretically having a wide viewing angle and response speed which has low dependency on a gray scale can be obtained.

The pixel shown in FIG. 27A includes a scan line 10601, a video signal line 10602, a common electrode 10603, a transistor 10604, and a pixel electrode 10605.

The scan line 10601 has a function of transmitting a signal (a scan signal) to the pixel. The image signal line 10602 has a function of transmitting a signal (an image signal) to the pixel. Note that since the scan line 10601 and the image signal line 10602 are arranged in matrix, they are formed of conductive layers in different layers. Note that a semiconductor layer may be provided at an intersection of the scan line 10601 and the image signal line 10602. Thus, intersection capacitance formed between the scan line 10601 and the image signal line 10602 can be reduced. Note that the image signal line 10602 is formed in accordance with a shape of the pixel electrode 10605.

The common electrode 10603 is provided in parallel to the pixel electrode 10605. The common electrode 10603 is an electrode for generating a horizontal electric field. Note that the common electrode 10603 is bent comb-shaped. Note that part of the common electrode 10603 is extended along the image signal line 10602 so as to surround the image signal line 10602. Thus, crosstalk can be reduced. Crosstalk is a phenomenon in which a potential of an electrode, which should hold the potential, is changed in accordance with change in potential of the image signal line 10602. Note that intersection capacitance can be reduced by providing a semiconductor layer between the common electrode 10603 and the image signal line 10602. Par of the common electrode 10603, which is provided in parallel to the scan line 10601, is formed of a material which is similar to that of the scan line 10601. Part of the common electrode 10603, which is provided in parallel to the pixel electrode 10605, is formed of a material which is similar to that of the pixel electrode 10605.

The transistor 10604 has a function as a switch which turns on the image signal line 10602 and the pixel electrode 10605. Note that one of a source region and a drain region of the transistor 10604 is provided so as to be surrounded by the other of the source region and the drain region of the transistor 10604. Thus, the channel width of the transistor 10604 increases, so that switching capability can be improved. Note that a gate electrode of the transistor 10604 is provided so as to surround the semiconductor layer.

The pixel electrode 10605 is electrically connected to one of a source electrode and a drain electrode of the transistor 10604. The pixel electrode 10605 is an electrode for applying signal voltage which is transmitted by the image signal line 10602 to a liquid crystal element. Note that the pixel electrode 10605 is bent comb-shaped. Thus, a horizontal electric field can be applied to liquid crystal molecules. In addition, since a plurality of regions having different alignment of the liquid crystal molecules can be formed, a viewing angle can be improved. Note that as the pixel electrode 10605, a light-transmitting material or a reflective material may be used. Alternatively, the pixel electrode 10605 may be formed by combining a light-transmitting material and a reflective material.

Note that a comb-shaped portion in the common electrode 10603 and the pixel electrode 10605 may be formed of different conductive layers. For example, the comb-shaped portion in the common electrode 10603 may be formed of a conductive layer which is the same as that of the scan line 10601 or the image signal line 10602. Similarly, the pixel electrode 10605 may be formed of a conductive layer which is the same as that of the scan line 10601 or the image signal line 10602.

FIG. 27B is a top plan view of a pixel in the case where an FFS mode and a transistor are combined. By applying the pixel structure shown in FIG. 27B to a liquid crystal display device, a liquid crystal display device theoretically having a wide viewing angle and response speed which has low dependency on a gray scale can be obtained.

The pixel shown in FIG. 27B may include a scan line 10611, a video signal line 10612, a common electrode 10613, a transistor 10614, and a pixel electrode 10615.

The scan line 10611 has a function of transmitting a signal (a scan signal) to the pixel. The image signal line 10612 has a function of transmitting a signal (an image signal) to the pixel. Note that since the scan line 10611 and the image signal line 10612 are arranged in matrix, they are formed of conductive layers in different layers. Note that a semiconductor layer may be provided at an intersection of the scan line 10611 and the image signal line 10612. Thus, intersection capacitance formed between the scan line 10611 and the image signal line 10612 can be reduced. Note that the image signal line 10612 is formed in accordance with a shape of the pixel electrode 10615.

The common electrode 10613 is formed uniformly below the pixel electrode 10615 and below and between the pixel electrodes 10615. Note that as the common electrode 10613, either a light-transmitting material or a reflective material may be used. Alternatively, the common electrode 10613 may be formed by combining a material in which a light-transmitting material and a reflective material.

The transistor 10614 has a function as a switch which turns on the image signal line 10612 and the pixel electrode 10615. Note that one of a source region and a drain region of the transistor 10614 is provided so as to be surrounded by the other of the source region and the drain region of the transistor 10614. Thus, the channel width of the transistor 10614 increases, so that switching capability can be improved. Note that a gate electrode of the transistor 10614 is provided so as to surround the semiconductor layer.

The pixel electrode 10615 is electrically connected to one of a source electrode and a drain electrode of the transistor 10614. The pixel electrode 10615 is an electrode for applying signal voltage which is transmitted by the image signal line 10612 to a liquid crystal element. Note that the pixel electrode 10615 is bent comb-shaped. The comb-shaped pixel electrode 10615 is provided to be closer to a liquid crystal layer than a uniform portion of the common electrode 10613. Thus, a horizontal electric field can be applied to liquid crystal molecules. In addition, a plurality of regions having different alignment of the liquid crystal molecules can be formed, so that a viewing angle can be improved. Note that as the pixel electrode 10615, a light-transmitting material or a reflective material may be used. Alternatively, the pixel electrode 10615 may be formed by combining a light-transmitting material and a reflective material.

Note that although this embodiment mode is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment mode can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 6

In this embodiment mode, a peripheral portion of a liquid crystal panel is described.

FIG. 28 shows an example of a liquid crystal display device including a so-called edge-light type backlight unit 20101 and a liquid crystal panel 20107. An edge-light type corresponds to a type in which a light source is provided at an end of a backlight unit and fluorescence of the light source is emitted from the entire light-emitting surface. The edge-light type backlight unit is thin and can save power.

The backlight unit 20101 includes a diffusion plate 20102, a light guide plate 20103, a reflection plate 20104, a lamp reflector 20105, and a light source 20106.

The light source 20106 has a function of emitting light as necessary. For example, as the light source 20106, a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light-emitting diode, an inorganic EL element, an organic EL element, or the like is used. The lamp reflector 20105 has a function of efficiently guiding fluorescence from the light source 20106 to the light guide plate 20103. The light guide plate 20103 has a function of guiding light to the entire surface by total reflection of fluorescence. The diffusion plate 20102 has a function of reducing variations in brightness. The reflection plate 20104 has a function of reflecting light which is leaked from the light guide plate 20103 downward (a direction which is opposite to the liquid crystal panel 20107) to be reused.

Note that a control circuit for controlling luminance of the light source 20106 is connected to the backlight unit 20101. By using this control circuit, luminance of the light source 20106 can be controlled.

FIGS. 29A to 29D are views each showing a detailed structure of the edge-light type backlight unit. Note that description of a diffusion plate, a light guide plate, a reflection plate, and the like is omitted.

A backlight unit 20201 shown in FIG. 29A has a structure in which a cold cathode fluorescent lamp 20203 is used as a light source. In addition, a lamp reflector 20202 is provided to efficiently reflect light from the cold cathode fluorescent lamp 20203. Such a structure is often used for a large display device because luminance of light obtained from the cold cathode fluorescent lamp is high.

A backlight unit 20211 shown in FIG. 29B has a structure in which light-emitting diodes (LEDs) 20213 are used as light sources. For example, the light-emitting diodes (LEDs) 20213 which emit white light are provided at a predetermined interval. In addition, a lamp reflector 20212 is provided to efficiently reflect light from the light-emitting diodes (LEDs) 20213.

Since luminance of light-emitting diodes is high, a structure using light-emitting diodes is suitable for a large display device. Since light-emitting diodes are superior in color reproductivity, an arrangement area can be reduced. Therefore, a frame of a display device can be narrowed.

Note that in the case where light-emitting diodes are mounted on a large display device, the light-emitting diodes can be provided on a back side of the substrate. The light-emitting diodes of R, G, and B are sequentially provided at a predetermined interval. By providing the light-emitting diodes, color reproductivity can be improved.

A backlight unit 20221 shown in FIG. 44C has a structure in which light-emitting diodes (LEDs) 20223, light-emitting diodes (LEDs) 20224, and light-emitting diodes (LEDs) 20225 of R, G, and B are used as light sources. The light-emitting diodes (LEDs) 20223, the light-emitting diodes (LEDs) 20224, and the light-emitting diodes (LEDs) 20225 of R, G, and B are each provided at a predetermined interval. By using the light-emitting diodes (LEDs) 20223, the light-emitting diodes (LEDs) 20224, and the light-emitting diodes (LEDs) 20225 of R, G, and B, color reproductivity can be improved. In addition, a lamp reflector 20222 is provided to efficiently reflect light from the light-emitting diodes.

Since luminance of light-emitting diodes is high, a structure using light-emitting diodes is suitable for a large display device. Since light-emitting diodes are superior in color reproductivity, an arrangement area can be reduced. Therefore, a frame of a display device can be narrowed.

By sequentially making the light-emitting diodes of R, G, and B emit light in accordance with time, color display can be performed. This is a so-called field sequential mode.

Note that a light-emitting diode which emits white light can be combined with the light-emitting diodes (LEDs) 20223, the light-emitting diodes (LEDs) 20224, and the light-emitting diodes (LEDs) 20225 of R, G, and B.

Note that in the case where light-emitting diodes are mounted on a large display device, the light-emitting diodes can be provided on a back side of the substrate. The light-emitting diodes of R, G, and B are sequentially provided at a predetermined interval. By providing the light-emitting diodes, color reproductivity can be improved.

A backlight unit 20231 shown in FIG. 44D has a structure in which light-emitting diodes (LEDs) 20233, light-emitting diodes (LEDs) 20234, and light-emitting diodes (LEDs) 20235 of R, G, and B are used as light sources. For example, among the light-emitting diodes (LEDs) 20233, the light-emitting diodes (LEDs) 20234, and the light-emitting diodes (LEDs) 20235 of R, G, and B, a plurality of the light-emitting diodes of a color with low emission intensity (e.g., green) are provided. By using the light-emitting diodes (LEDs) 20233, the light-emitting diodes (LEDs) 20234, and the light-emitting diodes (LEDs) 20235 of R, G, and B, color reproductivity can be improved. In addition, a lamp reflector 20232 is provided to efficiently reflect light from the light-emitting diodes.

Since luminance of light-emitting diodes is high, a structure using light-emitting diodes is suitable for a large display device. Since light-emitting diodes are superior in color reproductivity, an arrangement area can be reduced. Therefore, a frame of a display device can be narrowed.

By sequentially making the light-emitting diodes of R, G, and B emit light in accordance with time, color display can be performed. This is a so-called field sequential mode.

Note that a light-emitting diode which emits white light can be combined with the light-emitting diodes (LEDs) 20233, the light-emitting diodes (LEDs) 20234, and the light-emitting diodes (LEDs) 20235 of R, G, and B.

Note that in the case where light-emitting diodes are mounted on a large display device, the light-emitting diodes can be provided on a back side of the substrate. The light-emitting diodes of R, G, and B are sequentially provided at a predetermined interval. By providing the light-emitting diodes, color reproductivity can be improved.

FIG. 32A shows an example of a liquid crystal display device including a so-called direct-type backlight unit 20500 and a liquid crystal panel 20505. A direct type corresponds to a type in which a light source is provided directly under a light-emitting surface and fluorescence of the light source is emitted from the entire light-emitting surface. The direct-type backlight unit can efficiently utilize the amount of emitted light.

A backlight unit 20500 includes a diffusion plate 20501, a light-shielding plate 20502, a lamp reflector 20503, and a light source 20504.

The light source 20504 has a function of emitting light as necessary. For example, as the light source 20504, a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light-emitting diode, an inorganic EL element, an organic EL element, or the like is used. The lamp reflector 20503 has a function of efficiently guiding fluorescence from the light source 20504 to the diffusion plate 20501 and the light-shielding plate 20502. The light-shielding plate 20502 has a function of reducing variations in luminance by shielding much light as light becomes more intense in accordance with provision of the light source 20504. The diffusion plate 20501 also has a function of reducing variations in luminance.

A control circuit for controlling luminance of the light source 20504 is connected to the backlight unit 20500. By using this control circuit, luminance of the light source 20504 can be controlled.

FIG. 32B shows an example of a liquid crystal display device including a so-called direct-type backlight unit 20510 and a liquid crystal panel 20515. A direct type corresponds to a type in which a light source is provided directly under a light-emitting surface and fluorescence of the light source is emitted from the entire light-emitting surface. The direct-type backlight unit can efficiently utilize the amount of emitted light.

A backlight unit 20510 includes a diffusion plate 20511; a light-shielding plate 20512; a lamp reflector 20513; and a light source (R) 20514 a, a light source (G) 20514 b, and a light source (B) 20514 c of R, G, and B.

Each of the light source (R) 20514 a, the light source (G) 20514 b, and the light source (B) 20514 c of R, G, and B has a function of emitting light as necessary. For example, as each of the light source (R) 20514 a, the light source (G) 20514 b, and the light source (B) 20514 c, a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light-emitting diode, an inorganic EL element, an organic EL element, or the like is used. The lamp reflector 20513 has a function of efficiently guiding fluorescence from the light sources 20514 a to 20514 c to the diffusion plate 20511 and the light-shielding plate 20512. The light-shielding plate 20512 has a function of reducing variations in brightness or luminance by shielding much light as light becomes more intense in accordance with provision of the light sources 20514 a to 20514 c. The diffusion plate 20511 also has a function of reducing variations in brightness or luminance.

A control circuit for controlling luminance of the light source (R) 20514 a, the light source (G) 20514 b, and the light source (B) 20514 c of R, G, and B is connected to the backlight unit 20510. By using this control circuit, luminance of the light source (R) 20514 a, the light source (G) 20514 b, and the light source (B) 20514 c of R, G, and B can be controlled.

FIG. 30 shows an example of a structure of a polarizing plate (also referred to as a polarizing film).

A polarizing film 20300 includes a protective film 20301, a substrate film 20302, a PVA polarizing film 20303, a substrate film 20304, an adhesive layer 20305, and a mold release film 20306.

The PVA polarizing film 20303 has a function of generating light in only a certain vibration direction (linear polarized light). Specifically, the PVA polarizing film 20303 includes molecules, which function as a polarizer in which lengthwise electron density and widthwise electron density are greatly different from each other. The PVA polarizing film 20303 can generate linear polarized light by uniforming directions of the molecules in which lengthwise electron density and widthwise electron density are greatly different from each other.

For example, a high molecular film of poly vinyl alcohol is doped with an iodine compound and a PVA film is pulled in a certain direction, so that a film in which iodine molecules are aligned in a certain direction can be obtained as the PVA polarizing film 20303. Then, light which is parallel to a major axis of the iodine molecule is absorbed by the iodine molecule. Note that a dichroic dye may be used instead of iodine for high durability use and high heat resistance use. Note that it is preferable that the dye be used for a liquid crystal display device which needs to have durability and heat resistance, such as an in-car LCD or an LCD for a projector.

When the PVA polarizing film 20303 is sandwiched by films to be base materials (the substrate film 20302 and the substrate film 20304) from both sides, reliability can be improved. Note that the PVA polarizing film 20303 may be sandwiched by triacetylcellulose (TAC) films with high light-transmitting properties and high durability. Note that each of the substrate films and the TAC films function as protective films of polarizer included in the PVA polarizing film 20303.

The adhesive layer 20305 which is to be attached to a glass substrate of the liquid crystal panel is attached to one of the substrate films (the substrate film 20304). Note that the adhesive layer 20305 is formed by applying an adhesive to one of the substrate films (the substrate film 20304). The mold release film 20306 (a separate film) is provided to the adhesive layer 20305.

The protective film 20301 is provided to the other of the substrates films (the substrate film 20302).

A hard coating scattering layer (an anti-glare layer) may be provided on a surface of the polarizing film 20300. Since the surface of the hard coating scattering layer has minute unevenness formed by AG treatment and has an anti-glare function which scatters external light, reflection of external light in the liquid crystal panel can be prevented. Surface reflection can also be prevented.

Note that a treatment in which plurality of optical thin film layers having different refractive indexes are layered (also referred to as anti-reflection treatment or AR treatment) may be performed on the surface of the polarizing film 20300. The plurality of layered optical thin film layers having different refractive indexes can reduce reflectivity on the surface by an interference effect of light.

FIGS. 31A to 31C each show an example of a system block of the liquid crystal display device.

In a pixel portion 20405, signal lines 20412 which are extended from a signal line driver circuit 20403 are provided. In addition, in the pixel portion 20405, scan lines 20410 which are extended from a scan line driver circuit 20404 are also provided. In addition, a plurality of pixels are arranged in matrix in cross regions of the signal lines 20412 and the scan lines 20410. Note that each of the plurality of pixels includes a switching element. Therefore, voltage for controlling inclination of liquid crystal molecules can be separately input to each of the plurality of pixels. A structure in which a switching element is provided in each cross region in this manner is referred to as an active matrix type. Note that the present invention is not limited to such an active matrix type and a structure of a passive matrix type may be used. Since the passive matrix type does not have a switching element in each pixel, a process is simple.

A driver circuit portion 20408 includes a control circuit 20402, the signal line driver circuit 20403, and the scan line driver circuit 20404. An image signal 20401 is input to the control circuit 20402. The signal line driver circuit 20403 and the scan line driver circuit 20404 are controlled by the control circuit 20402 in accordance with this image signal 20401. That is, the control circuit 20402 inputs a control signal to each of the signal line driver circuit 20403 and the scan line driver circuit 20404. Then, in accordance with this control signal, the signal line driver circuit 20403 inputs a video signal to each of the signal lines 20412 and the scan line driver circuit 20404 inputs a scan signal to each of the scan lines 20410. Then, the switching element included in the pixel is selected in accordance with the scan signal and the video signal is input to a pixel electrode of the pixel.

Note that the control circuit 20402 also controls a power source 20407 in accordance with the image signal 20401. The power source 20407 includes a unit for supplying power to a lighting unit 20406. As the lighting unit 20406, an edge-light type backlight unit or a direct-type backlight unit can be used. Note that a front light may be used as the lighting unit 20406. A front light corresponds to a plate-like lighting unit including a luminous body and a light conducting body, which is attached to the front surface side of a pixel portion and illuminates the whole area. By using such a lighting unit, the pixel portion can be uniformly illuminated at low power consumption.

As shown in FIG. 31B, the scan line driver circuit 20404 includes a shift register 20441, a level shifter 20442, and a circuit functioning as a buffer 20443. A control signal such as a gate start pulse (GSP) or a gate clock signal (GCK) is input to the shift register 20441.

As shown in FIG. 31C, the signal line driver circuit 20403 includes a shift register 20431, a first latch 20432, a second latch 20433, a level shifter 20434, and a circuit functioning as a buffer 20435. The circuit functioning as the buffer 20435 corresponds to a circuit which has a function of amplifying a weak signal and includes an operational amplifier or the like. A control signal such as a source start pulse (SSP) or a source clock signal (SCK) is input to the level shifter 20434 and data (DATA) such as a video signal is input to the first latch 20432. Pieces of data (DATA) can be temporally held in the second latch 20433 and are simultaneously input to the pixel portion 20405 by a latch (LAT) signal. This is referred to as line sequential driving. Therefore, when a pixel is used in which not line sequential driving but dot sequential driving is performed, the second latch can be omitted.

Note that in this embodiment mode, a known liquid crystal panel can be used for the liquid crystal panel. For example, a structure in which a liquid crystal layer is sealed between two substrates can be used as the liquid crystal panel. A transistor, a capacitor, a pixel electrode, an alignment film, or the like is formed over one of the substrates. A polarizing plate, a retardation plate, or a prism sheet may be provided on the surface opposite to a top surface of the one of the substrates. A color filter, a black matrix, a counter electrode, an alignment film, or the like is provided on the other of the substrates. A polarizing plate or a retardation plate may be provided on the surface opposite to a top surface of the other of the substrates. The color filter and the black matrix may be formed over the top surface of the one of the substrates. Note that three-dimensional display can be performed by providing a slit (a grid) on the top surface side of the one of the substrates or the surface opposite to the top surface side of the one of the substrates.

Each of the polarizing plate, the retardation plate, and the prism sheet can be provided between the two substrates. Alternatively, each of the polarizing plate, the retardation plate, and the prism sheet can be integrated with one of the two substrates.

Note that although this embodiment mode is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment mode can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 7

In this embodiment mode, a driving method of a display device is described. In particular, a driving method of a liquid crystal display device is described.

First, overdriving is described with reference to FIGS. 33A to 33C. FIG. 33A shows time change in output luminance of a display element with respect to input voltage. Time change in output luminance of the display element with respect to input voltage 30121 represented by a dashed line is as shown by output luminance 30123 represented by a dashed line similarly. That is, although voltage for obtaining intended output luminance L_(o) is Vi, time in accordance with response speed of the element is necessary before output luminance reaches the intended output luminance L_(o) when Vi is directly input as input voltage.

Overdriving is a technique for increasing this response speed. Specifically, this is a method as follows: first, Vo which is larger voltage than Vi is applied to the element for a certain time to increase response speed of the element and output luminance is made close to the intended output luminance L_(o), and then, the input voltage is returned to Vi. The input voltage and the output luminance at this time are as shown by input voltage 30122 and output luminance 30124, respectively. In the graph of the output luminance 30124, time for reaching the intended output luminance L_(o) is shorter than that of the output luminance 30123.

Note that although the case where output luminance is changed positively with respect to input voltage is described in FIG. 33A, this embodiment mode also includes the case where output luminance is changed negatively with respect to input voltage.

A circuit for realizing such driving is described with reference to FIGS. 33B and 33C. First, the case where an input image signal 30131 is a signal having an analog value (may be a discrete value) and an output image signal 30132 is also a signal having an analog value is described with reference to FIG. 33B. An overdriving circuit shown in FIG. 33B includes an encoding circuit 30101, a frame memory 30102, a correction circuit 30103, and a D/A converter circuit 30104.

First, the input image signal 30131 is input to the encoding circuit 30101 and encoded. That is, the input image signal 30131 is converted from an analog signal into a digital signal with an appropriate bit number. After that, the converted digital signal is input to each of the frame memory 30102 and the correction circuit 30103. An image signal of the previous frame which is held in the frame memory 30102 is input to the correction circuit 30103 at the same time. Then, in the correction circuit 30103, an image signal corrected using an image signal of a frame and the image signal of the previous frame is output in accordance with a numeric value table which is prepared in advance. At this time, an output switching signal 30133 may be input to the correction circuit 30103 and the corrected image signal and the image signal of the frame may be switched to be output. Next, the corrected image signal or the image signal of the frame is input to the D/A converter circuit 30104. Then, the output image signal 30132 which is an analog signal having a value in accordance with the corrected image signal or the image signal of the frame is output. In this manner, overdriving is realized.

Next, the case where the input image signal 30131 is a signal having a digital value and the output image signal 30132 is also a signal having a digital value is described with reference to FIG. 33C. An overdriving circuit shown in FIG. 33C includes a frame memory 30112 and a correction circuit 30113.

First, the input image signal 30131 is a digital signal and is input to each of the frame memory 30112 and the correction circuit 30113. An image signal of the previous frame which is held in the frame memory 30112 is input to the correction circuit 30113 at the same time. Then, in the correction circuit 30113, an image signal corrected using an image signal of a frame and the image signal of the previous frame is output in accordance with a numeric value table which is prepared in advance. At this time, the output switching signal 30133 may be input to the correction circuit 30113 and the corrected image signal and the image signal of the frame may be switched to be output. In this manner, overdriving is realized.

Note that the case where the input image signal 30131 is an analog signal and the output image signal 30132 is a digital signal is included in the overdriving circuit in this embodiment mode. At this time, the D/A converter circuit 30104 is omitted from the circuit shown in FIG. 33B. In addition, the case where the input image signal 30131 is a digital signal and the output image signal 30132 is an analog signal is included in the overdriving circuit in this embodiment mode. At this time, the encoding circuit 30101 is omitted from the circuit shown in FIG. 33B.

Driving which controls a potential of a common line is described with reference to FIGS. 34A and 34B. FIG. 34A is a diagram showing a plurality of pixel circuits in which one common line is provided with respect to one scan line in a display device using a display element which has capacitive properties like a liquid crystal element. Each of the pixel circuits shown in FIG. 34A includes a transistor 30201, an auxiliary capacitor 30202, a display element 30203, a video signal line 30204, a scan line 30205, and a common line 30206.

A gate electrode of the transistor 30201 is electrically connected to the scan line 30205; one of a source electrode and a drain electrode of the transistor 30201 is electrically connected to the video signal line 30204; and the other of the source electrode and the drain electrode of the transistor 30201 is electrically connected to one of electrodes of the auxiliary capacitor 30202 and one of electrodes of the display element 30203. In addition, the other of the electrodes of the auxiliary capacitor 30202 is electrically connected to the common line 30206.

First, in each of pixels selected by the scan line 30205, voltage corresponding to an image signal is applied to the display element 30203 and the auxiliary capacitor 30202 through the video signal line 30204 because the transistor 30201 is turned on. At this time, when the image signal is a signal which makes all of pixels connected to the common line 30206 display a minimum gray scale or when the image signal is a signal which makes all of the pixels connected to the common line 30206 display a maximum gray scale, it is not necessary that the image signal be written to each of the pixels through the video signal line 30204. Voltage applied to the display element 30203 can be changed by changing a potential of the common line 30206 instead of writing the image signal through the video signal line 30204.

Next, FIG. 34B is a diagram showing a plurality of pixel circuits in which two common lines are provided with respect to one scan line in a display device using a display element which has capacitive properties like a liquid crystal element. Each of the pixel circuits shown in FIG. 34B includes a transistor 30211, an auxiliary capacitor 30212, a display element 30213, a video signal line 30214, a scan line 30215, a first common line 30216, and a second common line 30217.

A gate electrode of the transistor 30211 is electrically connected to the scan line 30215; one of a source electrode and a drain electrode of the transistor 30211 is electrically connected to the video signal line 30214; and the other of the source electrode and the drain electrode of the transistor 30211 is electrically connected to one of electrodes of the auxiliary capacitor 30212 and one of electrodes of the display element 30213. In addition, the other of the electrodes of the auxiliary capacitor 30212 is electrically connected to the first common line 30216. Further, in a pixel which is adjacent to the pixel, the other of the electrodes of the auxiliary capacitor 30212 is electrically connected to the second common line 30217.

In the pixel circuits shown in FIG. 34B, the number of pixels which are electrically connected to one common line is small. Therefore, by changing a potential of the first common line 30216 or the second common line 30217 instead of writing an image signal through the video signal line 30214, frequency of changing voltage applied to the display element 30213 is significantly increased. In addition, source inversion driving or dot inversion driving can be performed. By performing source inversion driving or dot inversion driving, reliability of the element can be improved and a flicker can be suppressed.

A scanning backlight is described with reference to FIGS. 35A to 35C. FIG. 35A is a view showing a scanning backlight in which cold cathode fluorescent lamps are arranged. The scanning backlight shown in FIG. 35A includes a diffusion plate 30301 and N pieces of cold cathode fluorescent lamps 30302-1 to 30302-N. The N pieces of the cold cathode fluorescent lamps 30302-1 to 30302-N are arranged on the back side of the diffusion plate 30301, so that the N pieces of the cold cathode fluorescent lamps 30302-1 to 30302-N can be scanned while luminance thereof is changed.

Change in luminance of each of the cold cathode fluorescent lamps in scanning is described with reference to FIG. 35C. First, luminance of the cold cathode fluorescent lamp 30302-1 is changed for a certain period. After that, luminance of the cold cathode fluorescent lamp 30302-2 which is provided adjacent to the cold cathode fluorescent lamp 30302-1 is changed for the same period. In this manner, luminance is changed sequentially from the cold cathode fluorescent lamp 30302-1 to the cold cathode fluorescent lamp 30302-N. Although luminance which is changed for a certain period is set to be lower than original luminance in FIG. 35C, it may also be higher than original luminance. In addition, although scanning is performed from the cold cathode fluorescent lamps 30302-1 to 30302-N, scanning may also be performed from the cold cathode fluorescent lamps 30302-N to 30302-1, which is in a reversed order.

By performing driving as in FIG. 35C, average luminance of the backlight can be decreased. Therefore, power consumption of the backlight, which mainly takes up power consumption of the liquid crystal display device, can be reduced.

Note that an LED may be used as a light source of the scanning backlight. The scanning backlight in that case is as shown in FIG. 35B. The scanning backlight shown in FIG. 35B includes a diffusion plate 30311 and light sources 30312-1 to 30312-N, in each of which LEDs are arranged. When the LED is used as the light source of the scanning backlight, there is an advantage in that the backlight can be thin and lightweight. In addition, there is also an advantage that a color reproduction area can be widened. Further, since the LEDs which are arranged in each of the light sources 30312-1 to 30312-N can be similarly scanned, a dot scanning backlight can also be obtained. By using the dot scanning backlight, quality of a moving image can be further improved.

Note that when the LED is used as the light source of the backlight, driving can be performed by changing luminance as shown in FIG. 35C.

Note that although this embodiment mode is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment mode can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 8

In this embodiment mode, a pixel structure and an operation of a pixel which can be applied to a liquid crystal display device are described.

In this embodiment mode, as an operation mode of a liquid crystal element, a TN (twisted nematic) mode, an IPS (in-plane-switching) mode, an FFS (fringe field switching) mode, an MVA (multi-domain vertical alignment) mode, a PVA (patterned vertical alignment) mode, an ASM (axially symmetric aligned micro-cell) mode, an OCB (optical compensated birefringence) mode, an FLC (ferroelectric liquid crystal) mode, an AFLC (antiferroelectric liquid crystal) mode, or the like can be used.

FIG. 36A shows an example of a pixel structure which can be applied to the liquid crystal display device.

A pixel 40100 includes a transistor 40101, a liquid crystal element 40102, and a capacitor 40103. A gate of the transistor 40101 is connected to a wiring 40105. A first electrode of the transistor 40101 is connected to a wiring 40104. A second electrode of the transistor 40101 is connected to a first electrode of the liquid crystal element 40102 and a first electrode of the capacitor 40103. A second electrode of the liquid crystal element 40102 corresponds to a counter electrode 40107. A second electrode of the capacitor 40103 is connected to a wiring 40106.

The wiring 40104 functions as a signal line. The wiring 40105 functions as a scan line. The wiring 40106 functions as a capacitor line. The transistor 40101 functions as a switch. The capacitor 40103 functions as a storage capacitor.

It is acceptable as long as the transistor 40101 functions as a switch, and the transistor 40101 may be either a P-channel transistor or an N-channel transistor.

A video signal is input to the wiring 40104. A scan signal is input to the wiring 40105. A constant potential is supplied to the wiring 40106. Note that the scan signal is an H-level or L-level digital voltage signal. In the case where the transistor 40101 is an N-channel transistor, an H level of the scan signal is a potential which can turn on the transistor 40101 and an L level of the scan signal is a potential which can turn off the transistor 40101. Alternatively, in the case where the transistor 40101 is a P-channel transistor, the H level of the scan signal is a potential which can turn off the transistor 40101 and the L level of the scan signal is a potential which can turn on the transistor 40101. Note that the video signal has analog voltage. The video signal has a potential which is lower than the H level of the scan signal and higher than the L level of the scan signal. Note that the constant potential supplied to the wiring 40106 is preferably equal to a potential of the counter electrode 40107.

Operations of the pixel 40100 are described by dividing the whole operations into the case where the transistor 40101 is on and the case where the transistor 40101 is off.

In the case where the transistor 40101 is on, the wiring 40104 is electrically connected to the first electrode (a pixel electrode) of the liquid crystal element 40102 and the first electrode of the capacitor 40103. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40102 and the first electrode of the capacitor 40103 from the wiring 40104 through the transistor 40101. In addition, the capacitor 40103 holds a potential difference between a potential of the video signal and the potential supplied to the wiring 40106.

In the case where the transistor 40101 is off, the wiring 40104 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40102 and the first electrode of the capacitor 40103. Therefore, each of the first electrode of the liquid crystal element 40102 and the first electrode of the capacitor 40103 is set in a floating state. Since the capacitor 40103 holds the potential difference between the potential of the video signal and the potential supplied to the wiring 40106, each of the first electrode of the liquid crystal element 40102 and the first electrode of the capacitor 40103 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40102 has transmissivity in accordance with the video signal.

FIG. 36B shows an example of a pixel structure which can be applied to the liquid crystal display device. In particular, FIG. 36B shows an example of a pixel structure which can be applied to a liquid crystal display device suitable for a horizontal electric field mode (including an IPS mode and an FFS mode).

A pixel 40110 includes a transistor 40111, a liquid crystal element 40112, and a capacitor 40113. A gate of the transistor 40111 is connected to a wiring 40115. A first electrode of the transistor 40111 is connected to a wiring 40114. A second electrode of the transistor 40111 is connected to a first electrode of the liquid crystal element 40112 and a first electrode of the capacitor 40113. A second electrode of the liquid crystal element 40112 is connected to a wiring 40116. A second electrode of the capacitor 40103 is connected to the wiring 40116.

The wiring 40114 functions as a signal line. The wiring 40115 functions as a scan line. The wiring 40116 functions as a capacitor line. The transistor 40111 functions as a switch. The capacitor 40113 functions as a storage capacitor.

It is acceptable as long as the transistor 40111 functions as a switch, and the transistor 40111 may be a P-channel transistor or an N-channel transistor.

A video signal is input to the wiring 40114. A scan signal is input to the wiring 40115. A constant potential is supplied to the wiring 40116. Note that the scan signal is an H-level or L-level digital voltage signal. In the case where the transistor 40111 is an N-channel transistor, an H level of the scan signal is a potential which can turn on the transistor 40111 and an L level of the scan signal is a potential which can turn off the transistor 40111. Alternatively, in the case where the transistor 40111 is a P-channel transistor, the H level of the scan signal is a potential which can turn off the transistor 40111 and the L level of the scan signal is a potential which can turn on the transistor 40111. Note that the video signal has analog voltage. The video signal has a potential which is lower than the H level of the scan signal and higher than the L level of the scan signal.

Operations of the pixel 40110 are described by dividing the whole operations into the case where the transistor 40111 is on and the case where the transistor 40111 is off.

In the case where the transistor 40111 is on, the wiring 40114 is electrically connected to the first electrode (a pixel electrode) of the liquid crystal element 40112 and the first electrode of the capacitor 40113. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40112 and the first electrode of the capacitor 40113 from the wiring 40114 through the transistor 40111. In addition, the capacitor 40113 holds a potential difference between a potential of the video signal and the potential supplied to the wiring 40116.

In the case where the transistor 40111 is off, the wiring 40114 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40112 and the first electrode of the capacitor 40113. Therefore, each of the first electrode of the liquid crystal element 40112 and the first electrode of the capacitor 40113 is set in a floating state. Since the capacitor 40113 holds the potential difference between the potential of the video signal and the potential supplied to the wiring 40116, each of the first electrode of the liquid crystal element 40112 and the first electrode of the capacitor 40113 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40112 has transmissivity in accordance with the video signal.

FIG. 37 shows an example of a pixel structure which can be applied to the liquid crystal display device. In particular, FIG. 37 shows an example of a pixel structure in which an aperture ratio of a pixel can be increased by reducing the number of wirings.

FIG. 37 shows two pixels which are provided in the same column direction (a pixel 40200 and a pixel 40210). For example, when the pixel 40200 is provided in an N-th row, the pixel 40210 is provided in an (N+1)th row.

A pixel 40200 includes a transistor 40201, a liquid crystal element 40202, and a capacitor 40203. A gate of the transistor 40201 is connected to a wiring 40205. A first electrode of the transistor 40201 is connected to a wiring 40204. A second electrode of the transistor 40201 is connected to a first electrode of the liquid crystal element 40202 and a first electrode of the capacitor 40203. A second electrode of the liquid crystal element 40202 corresponds to a counter electrode 40207. A second electrode of the capacitor 40203 is connected to a wiring which is the same as a wiring connected to a gate of a transistor of the previous row.

A pixel 40210 includes a transistor 40211, a liquid crystal element 40212, and a capacitor 40213. A gate of the transistor 40211 is connected to a wiring 40215. A first electrode of the transistor 40211 is connected to the wiring 40204. A second electrode of the transistor 40211 is connected to a first electrode of the liquid crystal element 40212 and a first electrode of the capacitor 40213. A second electrode of the liquid crystal element 40212 corresponds to a counter electrode 40217. A second electrode of the capacitor 40213 is connected to the wiring which is the same as the wiring connected to the gate of the transistor of the previous row (the wiring 40205).

The wiring 40204 functions as a signal line. The wiring 40205 functions as a scan line of the N-th row. The transistor 40201 functions as a switch. The capacitor 40203 functions as a storage capacitor.

The wiring 40215 functions as a scan line of the (N+1)th row. The transistor 40211 functions as a switch. The capacitor 40213 functions as a storage capacitor.

It is acceptable as long as each of the transistor 40201 and the transistor 40211 functions as a switch, and each of the transistor 40201 and the transistor 40211 may be either a P-channel transistor or an N-channel transistor.

A video signal is input to the wiring 40204. A scan signal (of an N-th row) is input to the wiring 40205. A scan signal (of an (N+1)th row) is input to the wiring 40215.

The scan signal is an H-level or L-level digital voltage signal. In the case where the transistor 40201 (or the transistor 40211) is an N-channel transistor, an H level of the scan signal is a potential which can turn on the transistor 40201 (or the transistor 40211) and an L level of the scan signal is a potential which can turn off the transistor 40201 (or the transistor 40211). Alternatively, in the case where the transistor 40201 (or the transistor 40211) is a P-channel transistor, the H level of the scan signal is a potential which can turn off the transistor 40201 (or the transistor 40211) and the L level of the scan signal is a potential which can turn on the transistor 40201 (or the transistor 40211). Note that the video signal has analog voltage. The video signal has a potential which is lower than the H level of the scan signal and higher than the L level of the scan signal.

Operations of the pixel 40200 are described by dividing the whole operations into the case where the transistor 40201 is on and the case where the transistor 40201 is off.

In the case where the transistor 40201 is on, the wiring 40204 is electrically connected to the first electrode (a pixel electrode) of the liquid crystal element 40202 and the first electrode of the capacitor 40203. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40202 and the first electrode of the capacitor 40203 from the wiring 40204 through the transistor 40201. In addition, the capacitor 40203 holds a potential difference between a potential of the video signal and a potential supplied to the wiring which is the same as the wiring connected to the gate of the transistor of the previous row.

In the case where the transistor 40201 is off, the wiring 40204 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40202 and the first electrode of the capacitor 40203. Therefore, each of the first electrode of the liquid crystal element 40202 and the first electrode of the capacitor 40203 is set in a floating state. Since the capacitor 40203 holds the potential difference between the potential of the video signal and the potential of the wiring which is the same as the wiring connected to the gate of the transistor of the previous row, each of the first electrode of the liquid crystal element 40202 and the first electrode of the capacitor 40203 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40202 has transmissivity in accordance with the video signal.

Operations of the pixel 40210 are described by dividing the whole operations into the case where the transistor 40211 is on and the case where the transistor 40211 is off.

In the case where the transistor 40211 is on, the wiring 40214 is electrically connected to the first electrode (a pixel electrode) of the liquid crystal element 40212 and the first electrode of the capacitor 40213. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40212 and the first electrode of the capacitor 40213 from the wiring 40214 through the transistor 40211. In addition, the capacitor 40213 holds a potential difference between a potential of the video signal and a potential supplied to a wiring which is the same as the wiring connected to the gate of the transistor of the previous row (the wiring 40205).

In the case where the transistor 40211 is off, the wiring 40214 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40212 and the first electrode of the capacitor 40213. Therefore, each of the first electrode of the liquid crystal element 40212 and the first electrode of the capacitor 40213 is set in a floating state. Since the capacitor 40103 holds the potential difference between the potential of the video signal and the potential of the wiring which is the same as the wiring connected to the gate of the transistor of the previous row (the wiring 40215), each of the first electrode (the pixel electrode) of the liquid crystal element 40212 and the first electrode of the capacitor 40213 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40212 has transmissivity in accordance with the video signal.

FIG. 38 shows an example of a pixel structure which can be applied to the liquid crystal display device. In particular, FIG. 38 shows an example of a pixel structure in which a viewing angle can be improved by using a subpixel.

A pixel 40320 includes a subpixel 40300 and a subpixel 40310. Although the case in which the pixel 40320 includes two subpixels is described, the pixel 40320 may include three or more subpixels.

The subpixel 40300 includes a transistor 40301, a liquid crystal element 40302, and a capacitor 40303. A gate of the transistor 40301 is connected to a wiring 40305. A first electrode of the transistor 40301 is connected to a wiring 40304. A second electrode of the transistor 40301 is connected to a first electrode of the liquid crystal element 40302 and a first electrode of the capacitor 40303. A second electrode of the liquid crystal element 40302 corresponds to a counter electrode 40307. A second electrode of the capacitor 40303 is connected to a wiring 40306.

The subpixel 40310 includes a transistor 40311, a liquid crystal element 40312, and a capacitor 40313. A gate of the transistor 40311 is connected to a wiring 40315. A first electrode of the transistor 40311 is connected to the wiring 40304. A second electrode of the transistor 40311 is connected to a first electrode of the liquid crystal element 40312 and a first electrode of the capacitor 40313. A second electrode of the liquid crystal element 40312 corresponds to a counter electrode 40317. A second electrode of the capacitor 40313 is connected to a wiring 40306.

The wiring 40304 functions as a signal line. The wiring 40305 functions as a scan line. The wiring 40315 functions as a signal line. The wiring 40306 functions as a capacitor line. Each of the transistor 40301 and the transistor 40311 functions as a switch. Each of the capacitor 40303 and the capacitor 40313 functions as a storage capacitor.

It is acceptable as long as each of the transistor 40301 and the transistor 40311 functions as a switch, and each of the transistor 40301 and the transistor 40311 may be either a P-channel transistor or an N-channel transistor.

A video signal is input to the wiring 40304. A scan signal is input to the wiring 40305. A scan signal is input to the wiring 40315. A constant potential is supplied to the wiring 40306.

The scan signal is an H-level or L-level digital voltage signal. In the case where the transistor 40301 (or the transistor 40311) is an N-channel transistor, an H level of the scan signal is a potential which can turn on the transistor 40301 (or the transistor 40311) and an L level of the scan signal is a potential which can turn off the transistor 40301 (or the transistor 40311). Alternatively, in the case where the transistor 40301 (or the transistor 40311) is a P-channel transistor, the H level of the scan signal is a potential which can turn off the transistor 40301 (or the transistor 40311) and the L level of the scan signal is a potential which can turn on the transistor 40301 (or the transistor 40311). Note that the video signal has analog voltage. The video signal has a potential which is lower than the H level of the scan signal and higher than the L level of the scan signal. Note that the constant potential supplied to the wiring 40306 is preferably equal to a potential of the counter electrode 40307.

Operations of the pixel 40320 are described by dividing the whole operations into the case where the transistor 40301 is on and the transistor 40311 is off, the case where the transistor 40301 is off and the transistor 40311 is on, and the case where the transistor 40301 and the transistor 40311 are off.

In the case where the transistor 40301 is on and the transistor 40311 is off, the wiring 40304 is electrically connected to the first electrode (a pixel electrode) of the liquid crystal element 40302 and the first electrode of the capacitor 40303 in the subpixel 40300. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40302 and the first electrode of the capacitor 40303 from the wiring 40304 through the transistor 40301. In addition, the capacitor 40303 holds a potential difference between a potential of the video signal and a potential supplied to the wiring 40306. At this time, the wiring 40304 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40312 and the first electrode of the capacitor 40313 in the subpixel 40310. Therefore, the video signal is not input to the subpixel 40310.

In the case where the transistor 40301 is off and the transistor 40311 is on, the wiring 40304 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40302 and the first electrode of the capacitor 40303 in the subpixel 40300. Therefore, each of the first electrode of the liquid crystal element 40302 and the first electrode of the capacitor 40303 is set in a floating state. Since the capacitor 40303 holds the potential difference between the potential of the video signal and the potential supplied to the wiring 40306, each of the first electrode of the liquid crystal element 40302 and the first electrode of the capacitor 40303 holds a potential which is the same as (corresponds to) the video signal. At this time, the wiring 40304 is electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40312 and the first electrode of the capacitor 40313 in the subpixel 40310. Therefore, the video signal is input to the first electrode (the pixel electrode) of the liquid crystal element 40312 and the first electrode of the capacitor 40313 from the wiring 40304 through the transistor 40311. In addition, the capacitor 40313 holds a potential difference between a potential of the video signal and a potential supplied to the wiring 40306.

In the case where the transistor 40301 and the transistor 40311 are off, the wiring 40304 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40302 and the first electrode of the capacitor 40303 in the subpixel 40300. Therefore, each of the first electrode of the liquid crystal element 40302 and the first electrode of the capacitor 40303 is set in a floating state. Since the capacitor 40303 holds the potential difference between the potential of the video signal and the potential supplied to the wiring 40306, each of the first electrode of the liquid crystal element 40302 and the first electrode of the capacitor 40303 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40302 has transmissivity in accordance with the video signal. At this time, the wiring 40304 is not electrically connected to the first electrode (the pixel electrode) of the liquid crystal element 40312 and the first electrode of the capacitor 40313 similarly in the subpixel 40310. Therefore, each of the first electrode of the liquid crystal element 40312 and the first electrode of the capacitor 40313 is set in a floating state. Since the capacitor 40313 holds the potential difference between the potential of the video signal and the potential of the wiring 40316, each of the first electrode of the liquid crystal element 40312 and the first electrode of the capacitor 40313 holds a potential which is the same as (corresponds to) the video signal. Note that the liquid crystal element 40312 has transmissivity in accordance with the video signal.

A video signal input to the subpixel 40300 may be a value which is different from that of a video signal input to the subpixel 40310. In this case, the viewing angle can be widened because alignment of liquid crystal molecules of the liquid crystal element 40302 and alignment of liquid crystal molecules of the liquid crystal element 40312 can be varied from each other.

Although this embodiment mode is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment mode can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 9

In this embodiment mode, various liquid crystal modes are described.

First, various liquid crystal modes are described with reference to cross-sectional views.

FIGS. 39A and 39B are schematic views of cross sections of a TN mode.

A liquid crystal layer 50100 is held between a first substrate 50101 and a second substrate 50102 which are provided so as to be opposite to each other. A first electrode 50105 is formed on a top surface of the first substrate 50101. A second electrode 50106 is formed on a top surface of the second substrate 50102. A first polarizing plate 50103 is provided on a surface of the first substrate 50101, which does not face the liquid crystal layer. A second polarizing plate 50104 is provided on a surface of the second substrate 50102, which does not face the liquid crystal layer. Note that the first polarizing plate 50103 and the second polarizing plate 50104 are provided so as to be in a cross nicol state.

The first polarizing plate 50103 may be provided on the top surface of the first substrate 50101. The second polarizing plate 50104 may be provided on the top surface of the second substrate 50102.

It is acceptable as long as at least one of or both the first electrode 50105 and the second electrode 50106 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50105 and the second electrode 50106 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 39A is a schematic view of a cross section in the case where voltage is applied to the first electrode 50105 and the second electrode 50106 (referred to as a vertical electric field mode). Since liquid crystal molecules are aligned longitudinally, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50103 and the second polarizing plate 50104 are provided so as to be in a cross nicol state, light emitted from the backlight cannot pass through the substrate. Therefore, black display is performed.

Note that by controlling voltage applied to the first electrode 50105 and the second electrode 50106, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 39B is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50105 and the second electrode 50106. Since the liquid crystal molecules are aligned laterally and rotated in a plane, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50103 and the second polarizing plate 50104 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed. This is a so-called normally white mode.

A liquid crystal display device having a structure shown in FIG. 39A or FIG. 39B can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50101 side or a second substrate 50102 side.

It is acceptable as long as a known material is used for a liquid crystal material used for a TN mode.

FIGS. 40A and 40B are schematic views of cross sections of a VA mode. In the VA mode, liquid crystal molecules are aligned such that they are vertical to a substrate when there is no electric field.

A liquid crystal layer 50200 is held between a first substrate 50201 and a second substrate 50202 which are provided so as to be opposite to each other. A first electrode 50205 is formed on a top surface of the first substrate 50201. A second electrode 50206 is formed on a top surface of the second substrate 50202. A first polarizing plate 50203 is provided on a surface of the first substrate 50201, which does not face the liquid crystal layer. A second polarizing plate 50204 is provided on a surface of the second substrate 50202, which does not face the liquid crystal layer. Note that the first polarizing plate 50203 and the second polarizing plate 50204 are provided so as to be in a cross nicol state.

The first polarizing plate 50203 may be provided on the top surface of the first substrate 50201. The second polarizing plate 50204 may be provided on the top surface of the second substrate 50202.

It is acceptable as long as at least one of or both the first electrode 50205 and the second electrode 50206 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50205 and the second electrode 50206 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 40A is a schematic view of a cross section in the case where voltage is applied to the first electrode 50205 and the second electrode 50206 (referred to as a vertical electric field mode). Since liquid crystal molecules are aligned laterally, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50203 and the second polarizing plate 50204 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed.

Note that by controlling voltage applied to the first electrode 50205 and the second electrode 50206, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 40B is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50205 and the second electrode 50206. Since liquid crystal molecules are aligned longitudinally, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50203 and the second polarizing plate 50204 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed. This is a so-called normally black mode.

A liquid crystal display device having a structure shown in FIG. 40A or FIG. 40B can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50201 side or a second substrate 50202 side.

It is acceptable as long as a known material is used for a liquid crystal material used for a VA mode.

FIGS. 40C and 40D are schematic views of cross sections of an MVA mode. In the MVA mode, viewing angle dependency of each portion is compensated by each other.

A liquid crystal layer 50210 is held between a first substrate 50211 and a second substrate 50212 which are provided so as to be opposite to each other. A first electrode 50215 is formed on a top surface of the first substrate 50211. A second electrode 50216 is formed on a top surface of the second substrate 50212. A first protrusion 50217 for controlling alignment is formed on the first electrode 50215. A second protrusion 50218 for controlling alignment is formed over the second electrode 50216. A first polarizing plate 50213 is provided on a surface of the first substrate 50211, which does not face the liquid crystal layer. A second polarizing plate 50214 is provided on a surface of the second substrate 50212, which does not face the liquid crystal layer. Note that the first polarizing plate 50213 and the second polarizing plate 50214 are provided so as to be in a cross nicol state.

The first polarizing plate 50213 may be provided on the top surface of the first substrate 50211. The second polarizing plate 50214 may be provided on the top surface of the second substrate 50212.

It is acceptable as long as at least one of or both the first electrode 50215 and the second electrode 50216 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50215 and the second electrode 50216 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 40C is a schematic view of a cross section in the case where voltage is applied to the first electrode 50215 and the second electrode 50216 (referred to as a vertical electric field mode). Since liquid crystal molecules are aligned so as to tilt toward the first protrusion 50217 and the second protrusion 50218, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50213 and the second polarizing plate 50214 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed.

Note that by controlling voltage applied to the first electrode 50215 and the second electrode 50216, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 40D is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50215 and the second electrode 50216. Since liquid crystal molecules are aligned longitudinally, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50213 and the second polarizing plate 50214 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed. This is a so-called normally black mode.

A liquid crystal display device having a structure shown in FIG. 40C or FIG. 40D can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50211 side or a second substrate 50212 side.

It is acceptable as long as a known material is used for a liquid crystal material used for an MVA mode.

FIGS. 41A and 41B are schematic views of cross sections of an OCB mode. In the OCB mode, viewing angle dependency is low because alignment of liquid crystal molecules in a liquid crystal layer can be optically compensated. This state of the liquid crystal molecules is referred to as bend alignment.

A liquid crystal layer 50300 is held between a first substrate 50301 and a second substrate 50302 which are provided so as to be opposite to each other. A first electrode 50305 is formed on a top surface of the first substrate 50301. A second electrode 50306 is formed on a top surface of the second substrate 50302. A first polarizing plate 50303 is provided on a surface of the first substrate 50301, which does not face the liquid crystal layer. A second polarizing plate 50304 is provided on a surface of the second substrate 50302, which does not face the liquid crystal layer. Note that the first polarizing plate 50303 and the second polarizing plate 50304 are provided so as to be in a cross nicol state.

The first polarizing plate 50303 may be provided on the top surface of the first substrate 50301. The second polarizing plate 50304 may be provided on the top surface of the second substrate 50302.

It is acceptable as long as at least one of or both the first electrode 50305 and the second electrode 50306 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50305 and the second electrode 50306 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 41A is a schematic view of a cross section in the case where voltage is applied to the first electrode 50305 and the second electrode 50306 (referred to as a vertical electric field mode). Since liquid crystal molecules are aligned longitudinally, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50303 and the second polarizing plate 50304 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed.

Note that by controlling voltage applied to the first electrode 50305 and the second electrode 50306, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 41B is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50305 and the second electrode 50306. Since liquid crystal molecules are in a bend alignment state, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50303 and the second polarizing plate 50304 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed. This is a so-called normally white mode.

A liquid crystal display device having a structure shown in FIG. 41A or FIG. 41B can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50301 side or a second substrate 50302 side.

It is acceptable as long as a known material is used for a liquid crystal material used for an OCB mode.

FIGS. 41C and 41D are schematic views of cross sections of an FLC mode or an AFLC mode.

A liquid crystal layer 50310 is held between a first substrate 50311 and a second substrate 50312 which are provided so as to be opposite to each other. A first electrode 50315 is formed on a top surface of the first substrate 50311. A second electrode 50316 is formed on a top surface of the second substrate 50312. A first polarizing plate 50313 is provided on a surface of the first substrate 50311, which does not face the liquid crystal layer. A second polarizing plate 50314 is provided on a surface of the second substrate 50312, which does not face the liquid crystal layer. Note that the first polarizing plate 50313 and the second polarizing plate 50314 are provided so as to be in a cross nicol state.

The first polarizing plate 50313 may be provided on the top surface of the first substrate 50311. The second polarizing plate 50314 may be provided on the top surface of the second substrate 50312.

It is acceptable as long as at least one of or both the first electrode 50315 and the second electrode 50316 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50315 and the second electrode 50316 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 41C is a schematic view of a cross section in the case where voltage is applied to the first electrode 50315 and the second electrode 50316 (referred to as a vertical electric field mode). Since liquid crystal molecules are aligned laterally in a direction which is deviated from a rubbing direction, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50313 and the second polarizing plate 50314 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed.

Note that by controlling voltage applied to the first electrode 50315 and the second electrode 50316, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 41D is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50315 and the second electrode 50316. Since liquid crystal molecules are aligned laterally in a rubbing direction, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50313 and the second polarizing plate 50314 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed. This is a so-called normally black mode.

A liquid crystal display device having a structure shown in FIG. 41C or FIG. 41D can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50311 side or a second substrate 50312 side.

It is acceptable as long as a known material is used for a liquid crystal material used for an FLC mode or an AFLC mode.

FIGS. 42A and 42B are schematic views of cross sections of an IPS mode. In the IPS mode, alignment of liquid crystal molecules in a liquid crystal layer can be optically compensated, the liquid crystal molecules are constantly rotated in a plane parallel to a substrate, and a horizontal electric field method in which electrodes are provided only on one substrate side is used.

A liquid crystal layer 50400 is held between a first substrate 50401 and a second substrate 50402 which are provided so as to be opposite to each other. A first electrode 50405 and a second electrode 50406 are formed on a top surface of the second substrate 50402. A first polarizing plate 50403 is provided on a surface of the first substrate 50401, which does not face the liquid crystal layer. A second polarizing plate 50404 is provided on a surface of the second substrate 50402, which does not face the liquid crystal layer. Note that the first polarizing plate 50403 and the second polarizing plate 50404 are provided so as to be in a cross nicol state.

The first polarizing plate 50403 may be provided on the top surface of the first substrate 50401. The second polarizing plate 50404 may be provided on the top surface of the second substrate 50402.

It is acceptable as long as both the first electrode 50405 and the second electrode 50406 have light-transmitting properties. Alternatively, part of one of the first electrode 50405 and the second electrode 50406 may have reflectivity.

FIG. 42A is a schematic view of a cross section in the case where voltage is applied to the first electrode 50405 and the second electrode 50406 (referred to as a horizontal electric field mode). Since liquid crystal molecules are aligned along a line of electric force which is deviated from a rubbing direction, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50403 and the second polarizing plate 50404 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed.

Note that by controlling voltage applied to the first electrode 50405 and the second electrode 50406, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 42B is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50405 and the second electrode 50406. Since liquid crystal molecules are aligned laterally in a rubbing direction, light emitted from a backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50403 and the second polarizing plate 50404 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed. This is a so-called normally black mode.

A liquid crystal display device having a structure shown in FIG. 42A or FIG. 42B can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50401 side or a second substrate 50402 side.

It is acceptable as long as a known material is used for a liquid crystal material used for an IPS mode.

FIGS. 42C and 42D are schematic views of cross sections of an FFS mode. In the FFS mode, alignment of liquid crystal molecules in a liquid crystal layer can be optically compensated, the liquid crystal molecules are constantly rotated in a plane parallel to a substrate, and a horizontal electric field method in which electrodes are provided only on one substrate side is used.

A liquid crystal layer 50410 is held between a first substrate 50411 and a second substrate 50412 which are provided so as to be opposite to each other. A second electrode 50416 is formed on a top surface of the second substrate 50412. An insulating film 50417 is formed on a top surface of the second electrode 50416. A first electrode 50415 is formed over the insulating film 50417. A first polarizing plate 50413 is provided on a surface of the first substrate 50411, which does not face the liquid crystal layer. A second polarizing plate 50414 is provided on a surface of the second substrate 50412, which does not face the liquid crystal layer. Note that the first polarizing plate 50413 and the second polarizing plate 50414 are provided so as to be in a cross nicol state.

The first polarizing plate 50413 may be provided on the top surface of the first substrate 50411. The second polarizing plate 50414 may be provided on the top surface of the second substrate 50412.

It is acceptable as long as at least one of or both the first electrode 50415 and the second electrode 50416 have light-transmitting properties (a transmissive or reflective liquid crystal display device). Alternatively, both the first electrode 50415 and the second electrode 50416 may have light-transmitting properties, and part of one of the electrodes may have reflectivity (a semi-transmissive liquid crystal display device).

FIG. 42C is a schematic view of a cross section in the case where voltage is applied to the first electrode 50415 and the second electrode 50416 (referred to as a horizontal electric field mode). Since liquid crystal molecules are aligned along a line of electric force which is deviated from a rubbing direction, light emitted from a backlight is affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50413 and the second polarizing plate 50414 are provided so as to be in a cross nicol state, light emitted from the backlight passes through the substrate. Therefore, white display is performed.

Note that by controlling voltage applied to the first electrode 50415 and the second electrode 50416, conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

FIG. 42D is a schematic view of a cross section in the case where voltage is not applied to the first electrode 50415 and the second electrode 50416. Since liquid crystal molecules are aligned laterally in a rubbing direction, light emitted from the backlight is not affected by birefringence of the liquid crystal molecules. In addition, since the first polarizing plate 50413 and the second polarizing plate 50414 are provided so as to be in a cross nicol state, light emitted from the backlight does not pass through the substrate. Therefore, black display is performed. This is a so-called normally black mode.

A liquid crystal display device having a structure shown in FIG. 42C or FIG. 42D can perform full-color display by being provided with a color filter. The color filter can be provided on a first substrate 50411 side or a second substrate 50412 side.

It is acceptable as long as a known material is used for a liquid crystal material used for an FFS mode.

Next, various liquid crystal modes are described with reference to top plan views.

FIG. 43 is a top plan view of a pixel portion to which an MVA mode is applied. In the MVA mode, viewing angle dependency of each portion is compensated by each other.

FIG. 43 shows a first pixel electrode 50501, second pixel electrodes (50502 a, 50502 b, and 50502 c), and a protrusion 50503. The first pixel electrode 50501 is formed over the entire surface of a counter substrate. The protrusion 50503 is formed so as to be a dogleg shape. In addition, the second pixel electrodes (50502 a, 50502 b, and 50502 c) are formed over the first pixel electrode 50501 so as to have shapes corresponding to the protrusion 50503.

Opening portions of the second pixel electrodes (50502 a, 50502 b, and 50502 c) function like protrusions.

In the case where voltage is applied to the first pixel electrode 50501 and the second pixel electrodes (50502 a, 50502 b, and 50502 c) (referred to as a vertical electric field mode), liquid crystal molecules are aligned so as to tilt toward the opening portions of the second pixel electrodes (50502 a, 50502 b, and 50502 c) and the protrusion 50503. Since light emitted from a backlight passes through a substrate when a pair of polarizing plates is provided so as to be in a cross nicol state, white display is performed.

Note that by controlling voltage applied to the first pixel electrode 50501 and the second pixel electrodes (50502 a, 50502 b, and 50502 c), conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

In the case where voltage is not applied to the first pixel electrode 50501 and the second pixel electrodes (50502 a, 50502 b, and 50502 c), the liquid crystal molecules are aligned longitudinally. Since light emitted from the backlight does not pass through a panel when the pair of polarizing plates is provided so as to be in the cross nicol state, black display is performed. This is a so-called normally black mode.

It is acceptable as long as a known material is used for a liquid crystal material used for an MVA mode.

FIGS. 44A to 44D are top plan views of a pixel portion to which an IPS mode is applied. In the IPS mode, alignment of liquid crystal molecules in a liquid crystal layer can be optically compensated, the liquid crystal molecules are constantly rotated in a plane parallel to a substrate, and a horizontal electric field method in which electrodes are provided only on one substrate side is used.

In the IPS mode, a pair of electrodes is formed so as to have different shapes.

FIG. 44A shows a first pixel electrode 50601 and a second pixel electrode 50602. The first pixel electrode 50601 and the second pixel electrode 50602 are wavy shapes.

FIG. 44B shows a first pixel electrode 50611 and a second pixel electrode 50612. The first pixel electrode 50611 and the second pixel electrode 50612 have shapes having concentric openings.

FIG. 44C shows a first pixel electrode 50621 and a second pixel electrode 50622. The first pixel electrode 50621 and the second pixel electrode 50622 are comb shapes and partially overlap with each other.

FIG. 44D shows a first pixel electrode 50631 and a second pixel electrode 50632. The first pixel electrode 50631 and the second pixel electrode 50632 are comb shapes in which electrodes engage with each other.

In the case where voltage is applied to the first pixel electrodes (50601, 50611, 50621, and 50631) and the second pixel electrodes (50602, 50612, 50622, and 50623) (referred to as a horizontal electric field mode), liquid crystal molecules are aligned along a line of electric force which is deviated from a rubbing direction. Since light emitted from a backlight passes through a substrate when a pair of polarizing plates is provided so as to be in a cross nicol state, white display is performed.

Note that by controlling voltage applied to the first pixel electrodes (50601, 50611, 50621, and 50631) and the second pixel electrodes (50602, 50612, 50622, and 50623), conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

In the case where voltage is not applied to the first pixel electrodes (50601, 50611, 50621, and 50631) and the second pixel electrodes (50602, 50612, 50622, and 50623), the liquid crystal molecules are aligned laterally in the rubbing direction. Since light emitted from the backlight does not pass through the substrate when the pair of polarizing plates is provided so as to be in the cross nicol state, black display is performed. This is a so-called normally black mode.

It is acceptable as long as a known material be used for a liquid crystal material used for an IPS mode.

FIGS. 45A to 45D are top plan views of a pixel portion to which an FFS mode is applied. In the FFS mode, alignment of liquid crystal molecules in a liquid crystal layer can be optically compensated, the liquid crystal molecules are constantly rotated in a plane parallel to a substrate, and a horizontal electric field method in which electrodes are provided only on one substrate side is used.

In the FFS mode, a first electrode is formed over a top surface of a second electrode so as to be various shapes.

FIG. 45A shows a first pixel electrode 50701 and a second pixel electrode 50702. The first pixel electrode 50701 is a bent dogleg shape. The second pixel electrode 50702 is not necessarily patterned.

FIG. 45B shows a first pixel electrode 50711 and a second pixel electrode 50712. The first pixel electrode 50711 is a concentric shape. The second pixel electrode 50712 is not necessarily patterned.

FIG. 45C shows a first pixel electrode 50721 and a second pixel electrode 50722. The first pixel electrode 50721 is a winding shape. The second pixel electrode 50722 is not necessarily patterned.

FIG. 45D shows a first pixel electrode 50731 and a second pixel electrode 50732. The first pixel electrode 50731 is a comb shape. The second pixel electrode 50732 is not necessarily patterned.

In the case where voltage is applied to the first pixel electrodes (50701, 50711, 50721, and 50731) and the second pixel electrodes (50702, 50712, 50722, and 50723) (referred to as a horizontal electric field mode), liquid crystal molecules are aligned along a line of electric force which is deviated from a rubbing direction. Since light emitted from a backlight passes through a substrate when a pair of polarizing plates is provided so as to be in a cross nicol state, white display is performed.

Note that by controlling voltage applied to the first pixel electrodes (50701, 50711, 50721, and 50731) and the second pixel electrodes (50702, 50712, 50722, and 50723), conditions of the liquid crystal molecules can be controlled. Therefore, since the amount of light emitted from the backlight passing through the substrate can be controlled, predetermined image display can be performed.

In the case where voltage is not applied to the first pixel electrodes (50701, 50711, 50721, and 50731) and the second pixel electrodes (50702, 50712, 50722, and 50723), the liquid crystal molecules are aligned laterally in the rubbing direction. Since light emitted from the backlight does not pass through the substrate when the pair of polarizing plates is provided so as to be in the cross nicol state, black display is performed. This is a so-called normally black mode.

It is acceptable as long as a known material is used for a liquid crystal material used for an FFS mode.

Although this embodiment mode is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment mode can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 10

In this embodiment mode, a pixel structure of a display device is described. In particular, a pixel structure of a display device using an organic EL element is described.

FIG. 46A shows an example of a top plan view (a layout diagram) of a pixel including two transistors. FIG. 46B shows an example of a cross-sectional view along X-X′ in FIG. 46A.

FIG. 46A shows a first transistor 60105, a first wiring 60106, a second wiring 60107, a second transistor 60108, a third wiring 60111, a counter electrode 60112, a capacitor 60113, a pixel electrode 60115, a partition wall 60116, an organic conductive film 60117, an organic thin film 60118, and a substrate 60119. Note that it is preferable that the first transistor 60105 be used as a switching transistor, the first wiring 60106 as a gate signal line, the second wiring 60107 as a source signal line, the second transistor 60108 as a driving transistor, and the third wiring 60111 as a current supply line.

A gate electrode of the first transistor 60105 is electrically connected to the first wiring 60106. One of a source electrode and a drain electrode of the first transistor 60105 is electrically connected to the second wiring 60107. The other of the source electrode and the drain electrode of the first transistor 60105 is electrically connected to a gate electrode of the second transistor 60108 and one electrode of the capacitor 60113. Note that the gate electrode of the first transistor 60105 includes a plurality of gate electrodes. Accordingly, leakage current in the off state of the first transistor 60105 can be reduced.

One of a source electrode and a drain electrode of the second transistor 60108 is electrically connected to the third wiring 60111, and the other of the source electrode and the drain electrode of the second transistor 60108 is electrically connected to the pixel electrode 60115. Accordingly, current flowing to the pixel electrode 60115 can be controlled by the second transistor 60108.

The organic conductive film 60117 is provided over the pixel electrode 60115, and the organic thin film 60118 (an organic compound layer) is provided thereover. The counter electrode 60112 is provided over the organic thin film 60118 (the organic compound layer). Note that the counter electrode 60112 may be formed over the entire surface to be connected to all the pixels in common, or may be patterned using a shadow mask or the like.

Light emitted from the organic thin film 60118 (the organic compound layer) is transmitted through either the pixel electrode 60115 or the counter electrode 60112.

In FIG. 46B, the case where light is emitted to the pixel electrode side, that is, a side on which the transistor and the like are formed is referred to as bottom emission; and the case where light is emitted to the counter electrode side is referred to as top emission.

In the case of bottom emission, it is preferable that the pixel electrode 60115 be formed of a light-transmitting conductive film. On the other hand, in the case of top emission, it is preferable that the counter electrode 60112 be formed of a light-transmitting conductive film.

In a light-emitting device for color display, EL elements having respective light emission colors of RGB may be separately formed, or an EL element with a single color may be formed over an entire surface and light emission of RGB can be obtained by using a color filter.

Note that the structures shown in FIGS. 46A and 46B are examples, and various structures can be employed for a pixel layout, a cross-sectional structure, a stacking order of electrodes of an EL element, and the like, other than the structures shown in FIGS. 46A and 46B. Further, as a light-emitting element, various elements such as a crystalline element such as an LED, and an element formed of an inorganic thin film can be used as well as the element formed of the organic thin film shown in the drawing.

FIG. 47A shows an example of a top plan view (a layout diagram) of a pixel including three transistors. FIG. 47B shows an example of a cross-sectional view along X-X′ in FIG. 47A.

FIG. 47A shows a substrate 60200, a first wiring 60201, a second wiring 60202, a third wiring 60203, a fourth wiring 60204, a first transistor 60205, a second transistor 60206, a third transistor 60207, a pixel electrode 60208, a partition wall 60211, an organic conductive film 60212, an organic thin film 60213, and a counter electrode 60214. Note that it is preferable that the first wiring 60201 be used as a source signal line, the second wiring 60202 as a gate signal line for writing, the third wiring 60203 as a gate signal line for erasing, the fourth wiring 60204 as a current supply line, the first transistor 60205 as a switching transistor, the second transistor 60206 as an erasing transistor, and the third transistor 60207 as a driving transistor.

A gate electrode of the first transistor 60205 is electrically connected to the second wiring 60202. One of a source electrode and a drain electrode of the first transistor 60205 is electrically connected to the first wiring 60201. The other of the source electrode and the drain electrode of the first transistor 60205 is electrically connected to a gate electrode of the third transistor 60207. Note that the gate electrode of the first transistor 60205 includes a plurality of gate electrodes. Accordingly, leakage current in the off state of the first transistor 60205 can be reduced.

A gate electrode of the second transistor 60206 is electrically connected to the third wiring 60203. One of a source electrode and a drain electrode of the second transistor 60206 is electrically connected to the fourth wiring 60204. The other of the source electrode and the drain electrode of the second transistor 60206 is electrically connected to the gate electrode of the third transistor 60207. Note that the gate electrode of the second transistor 60206 includes a plurality of gate electrodes. Accordingly, leakage current in the off state of the second transistor 60206 can be reduced.

One of a source electrode and a drain electrode of the third transistor 60207 is electrically connected to the fourth wiring 60204, and the other of the source electrode and the drain electrode of the third transistor 60207 is electrically connected to the pixel electrode 60208. Accordingly, current flowing to the pixel electrode 60208 can be controlled by the third transistor 60207.

The organic conductive film 60212 is provided over the pixel electrode 60208, and the organic thin film 60213 (an organic compound layer) is provided thereover. The counter electrode 60214 is provided over the organic thin film 60213 (the organic compound layer). Note that the counter electrode 60214 may be formed over the entire surface to be connected to all the pixels in common, or may be patterned using a shadow mask or the like.

Light emitted from the organic thin film 60213 (the organic compound layer) is transmitted through either the pixel electrode 60208 or the counter electrode 60214.

In FIG. 47B, the case where light is emitted to the pixel electrode side, that is, a side on which the transistor and the like are formed is referred to as bottom emission; and the case where light is emitted to the counter electrode side is referred to as top emission.

In the case of bottom emission, it is preferable that the pixel electrode 60208 be formed of a light-transmitting conductive film. On the other hand, in the case of top emission, it is preferable that the counter electrode 60214 be formed of a light-transmitting conductive film.

In a light-emitting device for color display, EL elements having respective light emission colors of RGB may be separately formed, or an EL element with a single color may be formed over an entire surface and light emission of RGB can be obtained by using a color filter.

Note that the structures shown in FIGS. 47A and 47B are examples, and various structures can be employed for a pixel layout, a cross-sectional structure, a stacking order of electrodes of an EL element, and the like, other than the structures shown in FIGS. 47A and 47B. Further, as a light-emitting element, various elements such as a crystalline element such as an LED, and an element formed of an inorganic thin film can be used as well as the element formed of the organic thin film shown in the drawing.

FIG. 48A shows an example of a top plan view (a layout diagram) of a pixel including four transistors. FIG. 48B shows an example of a cross-sectional view along X-X′ in FIG. 48A.

FIG. 48A shows a substrate 60300, a first wiring 60301, a second wiring 60302, a third wiring 60303, a fourth wiring 60304, a first transistor 60305, a second transistor 60306, a third transistor 60307, a fourth transistor 60308, a pixel electrode 60309, a fifth wiring 60311, a sixth wiring 60312, a partition wall 60321, an organic conductive film 60322, an organic thin film 60323, and a counter electrode 60324. Note that it is preferable that the first wiring 60301 be used as a source signal line, the second wiring 60302 as a gate signal line for writing, the third wiring 60303 as a gate signal line for erasing, the fourth wiring 60304 as a signal line for reverse bias, the first transistor 60305 as a switching transistor, the second transistor 60306 as an erasing transistor, the third transistor 60307 as a driving transistor, the fourth transistor 60308 as a transistor for reverse bias, the fifth wiring 60311 as a current supply line, and the sixth wiring 60312 as a power supply line for reverse bias.

A gate electrode of the first transistor 60305 is electrically connected to the second wiring 60302. One of a source electrode and a drain electrode of the first transistor 60305 is electrically connected to the first wiring 60301. The other of the source electrode and the drain electrode of the first transistor 60305 is electrically connected to a gate electrode of the third transistor 60307. Note that the gate electrode of the first transistor 60305 includes a plurality of gate electrodes. Accordingly, leakage current in the off state of the first transistor 60305 can be reduced.

A gate electrode of the second transistor 60306 is electrically connected to the third wiring 60303. One of a source electrode and a drain electrode of the second transistor 60306 is electrically connected to the fifth wiring 60311. The other of the source electrode and the drain electrode of the second transistor 60306 is electrically connected to the gate electrode of the third transistor 60307. Note that the gate electrode of the second transistor 60306 includes a plurality of gate electrodes. Accordingly, leakage current in the off state of the second transistor 60306 can be reduced.

One of a source electrode and a drain electrode of the third transistor 60307 is electrically connected to the fifth wiring 60311, and the other of the source electrode and the drain electrode of the third transistor 60307 is electrically connected to the pixel electrode 60309. Accordingly, current flowing to the pixel electrode 60309 can be controlled by the third transistor 60307.

A gate electrode of the fourth transistor 60308 is electrically connected to the fourth wiring 60304. One of a source electrode and a drain electrode of the fourth transistor 60308 is electrically connected to the sixth wiring 60312. The other of the source electrode and the drain electrode of the fourth transistor 60308 is electrically connected to the pixel electrode 60309. Accordingly, a potential of the pixel electrode 60309 can be controlled by the fourth transistor 60308, so that reverse bias can be applied to the organic conductive film 60322 and the organic thin film 60323. When reverse bias is applied to a light-emitting element including the organic conductive film 60322, the organic thin film 60323, and the like, reliability of the light-emitting element can be significantly improved.

The organic conductive film 60322 is provided over the pixel electrode 60309, and the organic thin film 60323 (an organic compound layer) is provided thereover. The counter electrode 60324 is provided over the organic thin film 60213 (the organic compound layer). Note that the counter electrode 60324 may be formed over the entire surface to be connected to all the pixels in common, or may be patterned using a shadow mask or the like.

Light emitted from the organic thin film 60323 (the organic compound layer) is transmitted through either the pixel electrode 60309 or the counter electrode 60324.

In FIG. 48B, the case where light is emitted to the pixel electrode side, that is, a side on which the transistor and the like are formed is referred to as bottom emission; and the case where light is emitted to the counter electrode side is referred to as top emission.

In the case of bottom emission, it is preferable that the pixel electrode 60309 be formed of a light-transmitting conductive film. On the other hand, in the case of top emission, it is preferable that the counter electrode 60324 be formed of a light-transmitting conductive film.

In a light-emitting device for color display, EL elements having respective light emission colors of RGB may be separately formed, or an EL element with a single color may be formed over an entire surface and light emission of RGB can be obtained by using a color filter.

Note that the structures shown in FIGS. 48A and 48B are examples, and various structures can be employed for a pixel layout, a cross-sectional structure, a stacking order of electrodes of an EL element, and the like, other than the structures shown in FIGS. 48A and 48B. Further, as a light-emitting element, various elements such as a crystalline element such as an LED, and an element formed of an inorganic thin film can be used as well as the element formed of the organic thin film shown in the drawing.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 11

In this embodiment mode, a structure and an operation of a pixel in a display device are described.

FIGS. 49A and 49B are timing charts showing an example of digital time gray scale driving. The timing chart of FIG. 49A shows a driving method in the case where a signal writing period (an address period) to a pixel and a light-emitting period (a sustain period) are separated.

One frame period refers to a period for fully displaying an image for one display region. One frame period includes a plurality of subframe periods, and one subframe period includes an address period and a sustain period. Address periods Ta1 to Ta4 indicate time for writing signals to pixels in all rows, and periods Tb1 to Tb4 indicate time for writing signals to pixels in one row (or one pixel). Sustain periods Ts1 to Ts4 indicate time for maintaining a lighting state or a non-lighting state in accordance with a video signal written to the pixel, and a ratio of the length of the sustain periods is set to satisfy Ts1:Ts2:Ts3:Ts4=2³:2²:2¹:2⁰=8:4:2:1. A gray scale is expressed depending on in which sustain period light emission is performed.

An operation is described. First, in the address period Ta1, pixel selection signals are sequentially input to scan lines from a first row, and a pixel is selected. Then, while the pixel is selected, a video signal is input to the pixel from a signal line. Then, when the video signal is written to the pixel, the pixel maintains the signal until a signal is input again. Lighting and non-lighting of each pixel in the sustain period Ts1 are controlled by the written video signal. Similarly, in the address periods Ta2, Ta3, and Ta4, a video signal is input to pixels, and lighting and non-lighting of each pixel in the sustain periods Ts2, Ts3, and Ts4 are controlled by the video signal. Then, in each subframe period, a pixel to which a signal for not lighting in the address period and for lighting when the sustain period starts after the address period ends is written is lit.

Here, the i-th pixel row is described with reference to FIG. 49B. First, in the address period Ta1, pixel selection signals are input to scan lines from a first row, and in a period Th1(i) in the address period Ta1, a pixel in the i-th row is selected. Then, while the pixel in the i-th row is selected, a video signal is input to the pixel in the i-th row from a signal line. Then, when the video signal is written to the pixel in the i-th row, the pixel in the i-th row maintains the signal until a signal is input again. Lighting and non-lighting of the pixel in the i-th row in the sustain period Ts1 are controlled by the written video signal. Similarly, in the address periods Ta2, Ta3, and Ta4, a video signal is input to the pixel in the i-th row, and lighting and non-lighting of the pixel in the i-th row in the sustain periods Ts2, Ts3, and Ts4 are controlled by the video signal. Then, in each subframe period, a pixel to which a signal for not lighting in the address period and for lighting when the sustain period starts after the address period ends is written is lit.

Here, the case where a 4-bit gray scale is expressed is described here; however, the number of bits and the number of gray scales are not limited thereto. Note that lighting is not needed to be performed in order of Ts1, Ts2, Ts3, and Ts4, and the order may be random or light may be emitted by dividing the whole period into a plurality of periods. A ratio of lighting time of Ts1, Ts2, Ts3, and Ts4 is not needed to be a power of two, and may be the same length or slightly different from a power of two.

Next, a driving method in the case where a period for writing a signal to a pixel (an address period) and a light-emitting period (a sustain period) are not separated is described. That is, a pixel in a row in which a writing operation of a video signal is completed maintains the signal until another signal is written to the pixel (or the signal is erased). A period between the writing operation and writing of another signal to the pixel is referred to as data holding time. In the data holding time, the pixel is lit or not lit in accordance with the video signal written to the pixel. The same operations are performed until the last row, and the address period ends. Then, an operation proceeds to a signal writing operation of the next subframe period sequentially from a row in which the data holding time ends.

As described above, in the case of a driving method in which a pixel is immediately lit or not lit in accordance with a video signal written to the pixel when the signal writing operation is completed and the data holding time starts, signals cannot be input to two rows at the same time. Accordingly, address periods need to be prevented from overlapping, so that the data holding time cannot be made shorter. As a result, it is difficult to perform high-level gray scale display.

Thus, the data holding time is set to be shorter than the address period by provision of an erasing period. A driving method in the case where the data holding time shorter than the address period is set by provision of an erasing period is described with reference to FIG. 50A.

First, in the address period Ta1, pixel scan signals are input to scan lines from a first row, and a pixel is selected. Then, while the pixel is selected, a video signal is input to the pixel from a signal line. Then, when the video signal is written to the pixel, the pixel maintains the signal until a signal is input again. Lighting and non-lighting of the pixel in the sustain period Ts1 are controlled by the written video signal. In a row in which a writing operation of a video signal is completed, a pixel is immediately lit or not lit in accordance with the written video signal. The same operations are performed until the last row, and the address period Ta1 ends. Then, an operation proceeds to a signal writing operation of the next subframe period sequentially from a row in which the data holding time ends. Similarly, in the address periods Ta2, Ta3, and Ta4, a video signal is input to the pixel, and lighting and non-lighting of the pixel in the sustain periods Ts2, Ts3, and Ts4 are controlled by the video signal. The end of the sustain period Ts4 is set by the start of an erasing operation. This is because when a signal written to a pixel is erased in an erasing time Te of each row, the pixel is forced to be not lit regardless of the video signal written to the pixel in the address period until another signal is written to the pixel. That is, the data holding time ends from a pixel in which the erasing time Te starts.

Here, the i-th pixel row is described with reference to FIG. 50B. In the address period Ta1, pixel scan signals are input to scan lines from a first row, and a pixel is selected. Then, in the period Th1(i), while the pixel in the i-th row is selected, a video signal is input to the pixel in the i-th row. Then, when the video signal is written to the pixel in the i-th row, the pixel in the i-th row maintains the signal until a signal is input again. Lighting and non-lighting of the pixel in the i-th row in a sustain period Ts1(i) are controlled by the written video signal. That is, the pixel in the i-th row is immediately lit or not lit in accordance with the video signal written to the pixel after the writing operation of the video signal to the i-th row is completed. Similarly, in the address periods Ta2, Ta3, and Ta4, a video signal is input to the pixel in the i-th row, and lighting and non-lighting of the pixel in the i-th row in the sustain periods Ts2, Ts3, and Ts4 are controlled by the video signal. The end of a sustain period Ts4(i) is set by the start of an erasing operation. This is because the pixel is forced to be not lit regardless of the video signal written to the pixel in the i-th row in an erasing time Te(i) in the i-th row. That is, the data holding time of the pixel in the i-th row ends when the erasing time Te(i) starts.

Thus, a display device with a high-level gray scale and a high duty ratio (a ratio of a lighting period in one frame period) can be provided, in which data holding time is shorter than an address period without separating the address period and a sustain period. Since instantaneous luminance can be lowered, reliability of a display element can be improved.

Here, the case where a 4-bit gray scale is expressed is described here; however, the number of bits and the number of gray scales are not limited thereto. Note that lighting is not needed to be performed in order of Ts1, Ts2, Ts3, and Ts4, and the order may be random or light may be emitted by dividing the whole period into a plurality of periods. A ratio of lighting time of Ts1, Ts2, Ts3, and Ts4 is not needed to be a power of two, and may be the same length or slightly different from a power of two.

Next, a structure and an operation of a pixel to which digital time gray scale driving can be applied are described.

FIG. 51 shows an example of a pixel structure to which digital time gray scale driving can be applied.

A pixel 80300 includes a switching transistor 80301, a driving transistor 80302, a light-emitting element 80304, and a capacitor 80303. A gate of the switching transistor 80301 is connected to a scan line 80306, a first electrode (one of a source electrode and a drain electrode) of the switching transistor 80301 is connected to a signal line 80305, and a second electrode (the other of the source electrode and the drain electrode) of the switching transistor 80301 is connected to a gate of the driving transistor 80302. The gate of the driving transistor 80302 is connected to a power supply line 80307 through the capacitor 80303, a first electrode of the driving transistor 80302 is connected to the power supply line 80307, and a second electrode of the driving transistor 80302 is connected to a first electrode (a pixel electrode) of the light-emitting element 80304. A second electrode of the light-emitting element 80304 corresponds to a common electrode 80308.

Note that the second electrode (the common electrode 80308) of the light-emitting element 80304 is set to have a low power supply potential. A low power supply potential refers to a potential satisfying (the low power supply potential)<(a high power supply potential) based on the high power supply potential set to the power supply line 80307. As the low power supply potential, GND, 0 V, or the like may be set, for example. In order to make the light-emitting element 80304 emit light by applying a potential difference between the high power supply potential and the low power supply potential to the light-emitting element 80304 so that current is supplied to the light-emitting element 80304, each of the potentials is set so that the potential difference between the high power supply potential and the low power supply potential is equal to or higher than forward threshold voltage.

Note that gate capacitance of the driving transistor 80302 may be used as a substitute for the capacitor 80303, so that the capacitor 80303 can be omitted. The gate capacitance of the driving transistor 80302 may be formed in a region where a source region, a drain region, an LDD region, or the like overlaps with the gate electrode. Alternatively, capacitance may be formed between a channel formation region and the gate electrode.

When a pixel is selected by the scan line 80306, that is, when the switching transistor 80301 is turned on, a video signal is input to the pixel from the signal line 80305. Then, a charge for voltage corresponding to the video signal is stored in the capacitor 80303, and the capacitor 80303 maintains the voltage. The voltage is voltage between the gate and the first electrode of the driving transistor 80302 and corresponds to gate-source voltage Vgs of the driving transistor 80302.

In general, an operation region of a transistor can be divided into a linear region and a saturation region. When drain-source voltage is denoted by Vds, gate-source voltage is denoted by Vgs, and threshold voltage is denoted by Vth, a boundary between the linear region and the saturation region sets so as to satisfy (Vgs−Vth)=Vds. In the case where (Vgs−Vth)>Vds is satisfied, the transistor operates in a linear region, and a current value is determined in accordance with the level of Vds and Vgs. On the other hand, in the case where (Vgs−Vth)<Vds is satisfied, the transistor operates in a saturation region and ideally, a current value hardly changes even when Vds changes. That is, the current value is determined only by the level of Vgs.

Here, in the case of a voltage-input voltage driving method, a video signal is input to the gate of the driving transistor 80302 so that the driving transistor 80302 is in either of two states of being sufficiently turned on and turned off. That is, the driving transistor 80302 operates in a linear region.

Thus, when a video signal which makes the driving transistor 80302 turned on is input, a power supply potential VDD set to the power supply line 80307 without change is ideally set to the first electrode of the light-emitting element 80304.

That is, ideally, constant voltage is applied to the light-emitting element 80304 to obtain constant luminance from the light-emitting element 80304. Then, a plurality of subframe periods are provided in one frame period. A video signal is written to a pixel in each subframe period, lighting and non-lighting of the pixel are controlled in each subframe period, and a gray scale is expressed by the sum of lighting subframe periods.

Note that when the video signal by which the driving transistor 80302 operates in a saturation region is input, current can be supplied to the light-emitting element 80304. When the light-emitting element 80304 is an element luminance of which is determined in accordance with current, luminance decay due to deterioration of the light-emitting element 80304 can be suppressed. Further, when the video signal is an analog signal, current in accordance with the video signal can be supplied to the light-emitting element 80304. In this case, analog gray scale driving can be performed.

FIG. 52 shows another example of a pixel structure to which digital time gray scale driving can be applied.

A pixel 80400 includes a switching transistor 80401, a driving transistor 80402, a capacitor 80403, a light-emitting element 80404, and a rectifying element 80409. A gate of the switching transistor 80401 is connected to a first scan line 80406, a first electrode (one of a source electrode and a drain electrode) of the switching transistor 80401 is connected to a signal line 80405, and a second electrode (the other of the source electrode and the drain electrode) of the switching transistor 80401 is connected to a gate of the driving transistor 80402. The gate of the driving transistor 80402 is connected to a power supply line 80407 through the capacitor 80403, and is also connected to a second scan line 80410 through the rectifying element 80409. A first electrode of the driving transistor 80402 is connected to the power supply line 80407, and a second electrode of the driving transistor 80402 is connected to a first electrode (a pixel electrode) of the light-emitting element 80404. A second electrode of the light-emitting element 80404 corresponds to a common electrode 80408.

The second electrode (the common electrode 80408) of the light-emitting element 80404 is set to have a low power supply potential. Note that a low power supply potential refers to a potential satisfying (the low power supply potential)<(a high power supply potential) based on the high power supply potential set to the power supply line 80407. As the low power supply potential, GND, 0 V, or the like may be set, for example. In order to make the light-emitting element 80404 emit light by applying a potential difference between the high power supply potential and the low power supply potential to the light-emitting element 80404 so that current is supplied to the light-emitting element 80404, each of the potentials is set so that the potential difference between the high power supply potential and the low power supply potential is equal to or higher than forward threshold voltage.

Note that gate capacitance of the driving transistor 80402 may be used as a substitute for the capacitor 80403, so that the capacitor 80403 can be omitted. The gate capacitance of the driving transistor 80402 may be formed in a region where a source region, a drain region, an LDD region, or the like overlaps with the gate electrode. Alternatively, capacitance may be formed between a channel formation region and the gate electrode.

As the rectifying element 80409, a diode-connected transistor can be used. A PN junction diode, a PIN junction diode, a Schottky diode, a diode formed of a carbon nanotube, or the like may be used other than a diode-connected transistor. A diode-connected transistor may be an n-channel transistor or a p-channel transistor.

The pixel 80400 is such that the rectifying element 80409 and the second scan line 80410 are added to the pixel shown in FIG. 51. Accordingly, the switching transistor 80401, the driving transistor 80402, the capacitor 80403, the light-emitting element 80404, the signal line 80405, the first scan line 80406, the power supply line 80407, and the common electrode 80408 shown in FIG. 52 correspond to the switching transistor 80301, the driving transistor 80302, the capacitor 80303, the light-emitting element 80304, the signal line 80305, the scan line 80306, the power supply line 80307, and the common electrode 80308 shown in FIG. 51. Accordingly, a writing operation and a light-emitting operation in FIG. 52 are similar to those described in FIG. 51, so that description thereof is omitted.

An erasing operation is described. In the erasing operation, an H-level signal is input to the second scan line 80410. Thus, current is supplied to the rectifying element 80409, and a gate potential of the driving transistor 80402 held by the capacitor 80403 can be set to a certain potential. That is, the potential of the gate of the driving transistor 80402 is set to a certain value, and the driving transistor 80402 can be forced to be turned off regardless of a video signal written to the pixel.

Note that an L-level signal input to the second scan line 80410 has a potential such that current is not supplied to the rectifying element 80409 when a video signal for non-lighting is written to a pixel. An H-level signal input to the second scan line 80410 has a potential such that a potential to turn off the driving transistor 80302 can be set to the gate regardless of a video signal written to a pixel.

FIG. 53 shows another example of a pixel structure to which digital time gray scale driving can be applied.

A pixel 80500 includes a switching transistor 80501, a driving transistor 80502, a capacitor 80503, a light-emitting element 80504, and an erasing transistor 80509. A gate of the switching transistor 80501 is connected to a first scan line 80506, a first electrode (one of a source electrode and a drain electrode) of the switching transistor 80501 is connected to a signal line 80505, and a second electrode (the other of the source electrode and the drain electrode) of the switching transistor 80501 is connected to a gate of the driving transistor 80502. The gate of the driving transistor 80502 is connected to a power supply line 80507 through the capacitor 80503, and is also connected to a first electrode of the erasing transistor 80509. A first electrode of the driving transistor 80502 is connected to the power supply line 80507, and a second electrode of the driving transistor 80502 is connected to a first electrode (a pixel electrode) of the light-emitting element 80504. A gate of the erasing transistor 80509 is connected to a second scan line 80510, and a second electrode of the erasing transistor 80509 is connected to the power supply line 80507. A second electrode of the light-emitting element 80504 corresponds to a common electrode 80508.

The second electrode (the common electrode 80508) of the light-emitting element 80504 is set to have a low power supply potential. Note that a low power supply potential refers to a potential satisfying (the low power supply potential)<(a high power supply potential) based on the high power supply potential set to the power supply line 80507. As the low power supply potential, GND, 0 V, or the like may be set, for example. In order to make the light-emitting element 80504 emit light by applying a potential difference between the high power supply potential and the low power supply potential to the light-emitting element 80504 so that current is supplied to the light-emitting element 80504, each of the potentials is set so that the potential difference between the high power supply potential and the low power supply potential is equal to or higher than forward threshold voltage.

Note that gate capacitance of the driving transistor 80502 may be used as a substitute for the capacitor 80503, so that the capacitor 80503 can be omitted. The gate capacitance of the driving transistor 80502 may be formed in a region where a source region, a drain region, an LDD region, or the like overlaps with the gate electrode. Alternatively, capacitance may be formed between a channel formation region and the gate electrode.

The pixel 80500 is such that the erasing transistor 80509 and the second scan line 80510 are added to the pixel shown in FIG. 51. Accordingly, the switching transistor 80501, the driving transistor 80502, the capacitor 80503, the light-emitting element 80504, the signal line 80505, the first scan line 80506, the power supply line 80507, and the common electrode 80508 shown in FIG. 53 correspond to the switching transistor 80301, the driving transistor 80302, the capacitor 80303, the light-emitting element 80304, the signal line 80305, the scan line 80306, the power supply line 80307, and the common electrode 80308 shown in FIG. 51. Accordingly, a writing operation and a light-emitting operation in FIG. 53 are similar to those described in FIG. 51, so that description thereof is omitted.

An erasing operation is described. In the erasing operation, an H-level signal is input to the second scan line 80510. Thus, the erasing transistor 80509 is turned on, and the gate and the first electrode of the driving transistor 80502 can be made to have the same potential. That is, Vgs of the driving transistor 80502 can be 0 V. Accordingly, the driving transistor 80502 can be forced to be turned off.

Next, a structure and an operation of a pixel called a threshold voltage compensation pixel are described. A threshold voltage compensation pixel can be applied to digital time gray scale driving and analog gray scale driving.

FIG. 54 shows an example of a structure of a pixel called a threshold voltage compensation pixel.

The pixel shown in FIG. 54 includes a driving transistor 80600, a first switch 80601, a second switch 80602, a third switch 80603, a first capacitor 80604, a second capacitor 80605, and a light-emitting element 80620. A gate of the driving transistor 80600 is connected to a signal line 80611 through the first capacitor 80604 and the first switch 80601 in this order. Further, the gate of the driving transistor 80600 is connected to a power supply line 80612 through the second capacitor 80605. A first electrode of the driving transistor 80600 is connected to the power supply line 80612. A second electrode of the driving transistor 80600 is connected to a first electrode of the light-emitting element 80620 through the third switch 80603. Further, the second electrode of the driving transistor 80600 is connected to the gate of the driving transistor 80600 through the second switch 80602. A second electrode of the light-emitting element 80620 corresponds to a common electrode 80621.

The second electrode of the light-emitting element 80620 is set to a low power supply potential. Note that a low power supply potential refers to a potential satisfying (the low power supply potential)<(a high power supply potential) based on the high power supply potential set to the power supply line 80612. As the low power supply potential, GND, 0 V, or the like may be set, for example. In order to make the light-emitting element 80620 emit light by applying a potential difference between the high power supply potential and the low power supply potential to the light-emitting element 80620 so that current is supplied to the light-emitting element 80620, each of the potentials is set so that the potential difference between the high power supply potential and the low power supply potential is equal to or higher than forward threshold voltage. Note that gate capacitance of the driving transistor 80600 may be used as a substitute for the second capacitor 80605, so that the second capacitor 80605 can be omitted. The gate capacitance of the driving transistor 80600 may be formed in a region where a source region, a drain region, an LDD region, or the like overlaps with the gate electrode. Alternatively, capacitance may be formed between a channel formation region and the gate electrode. Note that on/off of the first switch 80601, the second switch 80602, and the third switch 80603 is controlled by a first scan line 80613, a second scan line 80615, and a third scan line 80614, respectively.

A method for driving the pixel shown in FIG. 54 is described in which an operation period is divided into an initialization period, a data writing period, a threshold detecting period, and a light-emitting period.

In the initialization period, the second switch 80602 and the third switch 80603 are turned on. Then, a potential of the gate of the driving transistor 80600 is lower than at least a potential of the power supply line 80612. At this time, the first switch 80601 may be in an on state or an off state. Note that the initialization period is not necessarily required.

In the threshold detecting period, a pixel is selected by the first scan line 80613. That is, the first switch 80601 is turned on, and constant voltage is input from the signal line 80611. At this time, the second switch 80602 is turned on and the third switch 80603 is turned off. Accordingly, the driving transistor 80600 is diode-connected, and the second electrode and the gate of the driving transistor 80600 are placed in a floating state. Then, a potential of the gate of the driving transistor 80600 is a value obtained by subtracting threshold voltage of the driving transistor 80600 from the potential of the power supply line 80612. Thus, the threshold voltage of the driving transistor 80600 is held in the first capacitor 80604. A potential difference between the potential of the gate of the driving transistor 80600 and the constant voltage input from the signal line 80611 is held in the second capacitor 80605.

In the data writing period, a video signal (voltage) is input from the signal line 80611. At this time, the first switch 80601 is kept on, the second switch 80602 is turned off, and the third switch 80603 is kept off. Since the gate of the driving transistor 80600 is in a floating state, the potential of the gate of the driving transistor 80600 changes depending on a potential difference between the constant voltage input from the signal line 80611 in the threshold detecting period and the video signal input from the signal line 80611 in the data writing period. For example, when (a capacitance value of the first capacitor 80604)<<(a capacitance value of the second capacitor 80605) is satisfied, the potential of the gate of the driving transistor 80600 in the data writing period is approximately equal to the sum of a potential difference (the amount of change) between the potential of the signal line 80611 in the threshold detecting period and the potential of the signal line 80611 in the data writing period; and a value obtained by subtracting the threshold voltage of the driving transistor 80600 from the potential of the power supply line 80612. That is, the potential of the gate of the driving transistor 80600 becomes a potential obtained by correcting the threshold voltage of the driving transistor 80600.

In the light-emitting period, current in accordance with a potential difference (Vgs) between the gate of the driving transistor 80600 and the power supply line 80612 is supplied to the light-emitting element 80620. At this time, the first switch 80601 is turned off, the second switch 80602 is kept off, and the third switch 80603 is turned on. Note that current flowing to the light-emitting element 80620 is constant regardless of the threshold voltage of the driving transistor 80600.

Note that a pixel structure of the present invention is not limited to that shown in FIG. 54. For example, a switch, a resistor, a capacitor, a transistor, a logic circuit, or the like may be added to the pixel shown in FIG. 54. For example, the second switch 80602 may include a p-channel transistor or an n-channel transistor, the third switch 80603 may include a transistor with polarity different from that of the second switch 80602, and the second switch 80602 and the third switch 80603 may be controlled by the same scan line.

A structure and an operation of a pixel called a current input pixel are described. A current input pixel can be applied to digital gray scale driving and analog gray scale driving.

FIG. 55 shows an example of a structure of a current input pixel.

The pixel shown in FIG. 55 includes a driving transistor 80700, a first switch 80701, a second switch 80702, a third switch 80703, a capacitor 80704, and a light-emitting element 80730. A gate of the driving transistor 80700 is connected to a signal line 80711 through the second switch 80702 and the first switch 80701 in this order. Further, the gate of the driving transistor 80700 is connected to a power supply line 80712 through the capacitor 80704. A first electrode of the driving transistor 80700 is connected to the power supply line 80712. A second electrode of the driving transistor 80700 is connected to the signal line 80711 through the first switch 80701. Further, the second electrode of the driving transistor 80700 is connected to a first electrode of the light-emitting element 80730 through the third switch 80703. A second electrode of the light-emitting element 80730 corresponds to a common electrode 80731.

The second electrode of the light-emitting element 80730 is set to a low power supply potential. Note that a low power supply potential refers to a potential satisfying (the low power supply potential)<(a high power supply potential) based on the high power supply potential set to the power supply line 80712. As the low power supply potential, GND, 0 V, or the like may be set, for example. In order to make the light-emitting element 80730 emit light by applying a potential difference between the high power supply potential and the low power supply potential to the light-emitting element 80730 so that current is supplied to the light-emitting element 80730, each of the potentials is set so that the potential difference between the high power supply potential and the low power supply potential is equal to or higher than forward threshold voltage. Note that gate capacitance of the driving transistor 80700 may be used as a substitute for the capacitor 80704, so that the capacitor 80704 can be omitted. The gate capacitance of the driving transistor 80700 may be formed in a region where a source region, a drain region, an LDD region, or the like overlaps with the gate electrode. Alternatively, capacitance may be formed between a channel formation region and the gate electrode. Note that on/off of the first switch 80701, the second switch 80702, and the third switch 80703 is controlled by a first scan line 80713, a second scan line 80714, and a third scan line 80715, respectively.

A method for driving the pixel shown in FIG. 55 is described in which an operation period is divided into a data writing period and a light-emitting period.

In the data writing period, a pixel is selected by the first scan line 80713. That is, the first switch 80701 is turned on, and current is input as a video signal from the signal line 80711. At this time, the second switch 80702 is turned on and the third switch 80703 is turned off. Accordingly, a potential of the gate of the driving transistor 80700 becomes a potential in accordance with the video signal. That is, voltage between the gate electrode and the source electrode of the driving transistor 80700, which is such that the driving transistor 80700 supplies the same current as the video signal, is held in the capacitor 80704.

Next, in the light-emitting period, the first switch 80701 and the second switch 80702 are turned off, and the third switch 80703 is turned on. Thus, current with the same value as the video signal is supplied to the light-emitting element 80730.

Note that the present invention is not limited to the pixel structure shown in FIG. 55. For example, a switch, a resistor, a capacitor, a transistor, a logic circuit, or the like may be added to the pixel shown in FIG. 55. For example, the first switch 80701 may include a p-channel transistor or an n-channel transistor, the second switch 80702 may include a transistor with the same polarity as that of the first switch 80701, and the first switch 80701 and the second switch 80702 may be controlled by the same scan line. The second switch 80702 may be provided between the gate of the driving transistor 80700 and the signal line 80711.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 12

In this embodiment mode, a structure and a manufacturing method of a transistor are described.

FIGS. 56A to 56G show examples of structures and manufacturing methods of transistors included in a display device to which the present invention can be applied.

FIG. 56A shows structure examples of transistors included in the display device to which the present invention can be applied. FIGS. 56B to 56G show examples of manufacturing methods of the transistors included in the display device to which the present invention can be applied.

Note that the structure and the manufacturing method of the transistors included in the display device to which the present invention can be applied are not limited to those shown in FIGS. 56A to 56G, and various structures and manufacturing methods can be employed.

First, structure examples of transistors included in the display device to which the present invention can be applied are described with reference to FIG. 56A. FIG. 56A is a cross-sectional view of a plurality of transistors each having a different structure. Here, in FIG. 56A, the plurality of transistors each having a different structure are juxtaposed, which is for describing structures of the transistors. Accordingly, the transistors are not needed to be actually juxtaposed as shown in FIG. 56A and can be separately formed as needed.

Next, characteristics of each layer forming the transistor included in the display device to which the present invention can be applied are described.

A substrate 110111 can be a glass substrate using barium borosilicate glass, aluminoborosilicate glass, or the like, a quartz substrate, a ceramic substrate, a metal substrate containing stainless steel, or the like. Further, a substrate formed of plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or a substrate formed of a flexible synthetic resin such as acrylic can also be used. By using a flexible substrate, a display device capable of being bent can be formed. A flexible substrate has no strict limitations on the area or the shape of the substrate. Accordingly, for example, when a substrate having a rectangular shape, each side of which is 1 meter or more, is used as the substrate 110111, productivity can be significantly improved. Such an advantage is highly favorable as compared with the case where a circular silicon substrate is used.

An insulating film 110112 functions as a base film and is provided to prevent alkali metal such as Na or alkaline earth metal from the substrate 110111 from adversely affecting characteristics of a semiconductor element. The insulating film 110112 can have a single-layer structure or a stacked-layer structure of an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y). For example, when the insulating film 110112 is provided to have a two-layer structure, it is preferable that a silicon nitride oxide film be used as a first insulating film and a silicon oxynitride film be used as a second insulating film. Further, when the insulating film 110112 is provided to have a three-layer structure, it is preferable that a silicon oxynitride film be used as a first insulating film, a silicon nitride oxide film be used as a second insulating film, and a silicon oxynitride film be used as a third insulating film.

Semiconductor layers 110113, 110114, and 110115 can be formed using an amorphous semiconductor or a semi-amorphous semiconductor (SAS). Alternatively, a polycrystalline semiconductor layer may be used. SAS is a semiconductor having an intermediate structure between amorphous and crystalline (including single crystal and polycrystalline) structures and having a third state which is stable in free energy. Moreover, SAS includes a crystalline region with a short-range order and lattice distortion. A crystalline region of 0.5 to 20 nm can be observed at least in part of a film. When silicon is contained as a main component, Raman spectrum shifts to a wave number side lower than 520 cm⁻¹. The diffraction peaks of (111) and (220) which are thought to be contributed to a silicon crystalline lattice are observed by X-ray diffraction. SAS contains hydrogen or halogen of at least 1 atomic percent or more to compensate dangling bonds. SAS is formed by glow discharge decomposition (plasma CVD) of a material gas. As the material gas, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like as well as SiH₄ can be used. Alternatively, GeF₄ may be mixed. The material gas may be diluted with H₂, or H₂ and one or more kinds of rare gas elements selected from He, Ar, Kr, and Ne. A dilution ratio is in the range of 2 to 1000 times. Pressure is in the range of approximately 0.1 to 133 Pa, and a power supply frequency is 1 to 120 MHz, preferably 13 to 60 MHz. A substrate heating temperature may be 300° C. or lower. A concentration of impurities in atmospheric components such as oxygen, nitrogen, and carbon is preferably 1×10²⁰ cm⁻¹ or less as impurity elements in the film. In particular, an oxygen concentration is 5×10¹⁹/cm³ or less, preferably 1×10¹⁹/cm³ or less. Here, an amorphous semiconductor layer is formed using a material containing silicon (Si) as its main component (e.g., Si_(x)Ge_(1-x)) by a known method (such as a sputtering method, an LPCVD method, or a plasma CVD method). Then, the amorphous semiconductor layer is crystallized by a known crystallization method such as a laser crystallization method, a thermal crystallization method using RTA or an annealing furnace, or a thermal crystallization method using a metal element which promotes crystallization.

An insulating film 110116 can have a single-layer structure or a stacked-layer structure of an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y).

A gate electrode 110117 can have a single-layer structure of a conductive film or a stacked-layer structure of two or three conductive films. As a material for the gate electrode 110117, a known conductive film can be used. For example, a single film of an element such as tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), or silicon (Si); a nitride film containing the aforementioned element (typically, a tantalum nitride film, a tungsten nitride film, or a titanium nitride film); an alloy film in which the aforementioned elements are combined (typically, a Mo—W alloy or a Mo—Ta alloy); a silicide film containing the aforementioned element (typically, a tungsten silicide film or a titanium silicide film); and the like can be used. Note that the aforementioned single film, nitride film, alloy film, silicide film, and the like can have a single-layer structure or a stacked-layer structure.

An insulating film 110118 can have a single-layer structure or a stacked-layer structure of an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y); or a film containing carbon, such as a DLC (diamond-like carbon), by a known method (such as a sputtering method or a plasma CVD method).

An insulating film 110119 can have a single-layer structure or a stacked-layer structure of a siloxane resin; an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y); a film containing carbon, such as a DLC (diamond-like carbon); or an organic material such as epoxy, polyimide, polyamide, polyvinyl phenol, benzocyclobutene, or acrylic. Note that a siloxane resin corresponds to a resin having Si—O—Si bonds. Siloxane includes a skeleton structure of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used. Alternatively, a fluoro group, or a fluoro group and an organic group containing at least hydrogen can be used as a substituent. Note that in a display device applicable to the present invention, the insulating film 110119 can be directly provided so as to cover the gate electrode 110117 without provision of the insulating film 110118.

As a conductive film 110123, a single film of an element such as Al, Ni, C, W, Mo, Ti, Pt, Cu, Ta, Au, or Mn, a nitride film containing the aforementioned element, an alloy film in which the aforementioned elements are combined, a silicide film containing the aforementioned element, or the like can be used. For example, as an alloy containing a plurality of the aforementioned elements, an Al alloy containing C and Ti, an Al alloy containing Ni, an Al alloy containing C and Ni, an Al alloy containing C and Mn, or the like can be used. Further, when the conductive film has a stacked-layer structure, Al can be interposed between Mo, Ti, or the like; thus, resistance of Al to heat and chemical reaction can be improved.

Next, with reference to the cross-sectional view of the plurality of transistors each having a different structure shown in FIG. 56A, characteristics of each structure are described.

A transistor 110101 is a single drain transistor. Since the single drain transistor can be formed by a simple method, it is advantageous in low manufacturing cost and high yield. Here, the semiconductor layers 110113 and 110115 have different concentrations of impurities, and the semiconductor layer 110113 is used as a channel formation region and the semiconductor layers 110115 are used as a source region and a drain region. By controlling the concentration of impurities in this manner, resistivity of the semiconductor layer can be controlled. Further, an electrical connection state of the semiconductor layer and the conductive film 110123 can be closer to ohmic contact. Note that as a method of separately forming the semiconductor layers each having different amount of impurities, a method can be used in which impurities are doped in a semiconductor layer using the gate electrode 110117 as a mask.

A transistor 110102 is a transistor in which the gate electrode 110117 is tapered at an angle of at least certain degrees. Since the transistor can be formed by a simple method, it is advantageous in low manufacturing cost and high yield. Here, the semiconductor layers 110113, 110114, and 110115 have different concentrations of impurities. The semiconductor layer 110113 is used as a channel formation region, the semiconductor layers 110114 as lightly doped drain (LDD) regions, and the semiconductor layers 110115 as a source region and a drain region. By controlling the amount of impurities in this manner, resistivity of the semiconductor layer can be controlled. Further, an electrical connection state of the semiconductor layer and the conductive film 110123 can be closer to ohmic contact. Moreover, since the transistor includes the LDD regions, a high electric field is hardly applied inside the transistor, so that deterioration of the element due to hot carriers can be suppressed. Note that as a method of separately forming the semiconductor layers having different amount of impurities, a method can be used in which impurities are doped in a semiconductor layer using the gate electrode 110117 as a mask. In the transistor 110102, since the gate electrode 110117 is tapered at an angle of at least certain degrees, gradient of the concentration of impurities doped in the semiconductor layer through the gate electrode 110117 can be provided, and the LDD region can be easily formed.

A transistor 110103 is a transistor in which the gate electrode 110117 is formed of at least two layers and a lower gate electrode is longer than an upper gate electrode. In this specification, a shape of the lower and upper gate electrodes is called a hat shape. When the gate electrode 110117 has a hat shape, an LDD region can be formed without addition of a photomask. Note that a structure where the LDD region overlaps with the gate electrode 110117, like the transistor 110103, is particularly called a GOLD (gate overlapped LDD) structure. As a method of forming the gate electrode 110117 with a hat shape, the following method may be used.

First, when the gate electrode 110117 is patterned, the lower and upper gate electrodes are etched by dry etching so that side surfaces thereof are inclined (tapered). Then, the inclination of the upper gate electrode is processed to be almost perpendicular by anisotropic etching. Thus, the gate electrode a cross section of which is a hat shape is formed. After that, impurity elements are doped twice, so that the semiconductor layer 110113 used as the channel formation region, the semiconductor layers 110114 used as the LDD regions, and the semiconductor layers 110115 used as a source electrode and a drain electrode are formed.

Note that here, part of the LDD region, which overlaps with the gate electrode 110117, is referred to as an Lov region, and part of the LDD region, which does not overlap with the gate electrode 110117, is referred to as an Loff region. The Loff region is highly effective in suppressing an off-current value, whereas it is not very effective in preventing deterioration in an on-current value due to hot carriers by relieving an electric field in the vicinity of the drain. On the other hand, the Lov region is effective in preventing deterioration in the on-current value by relieving the electric field in the vicinity of the drain, whereas it is not very effective in suppressing the off-current value. Thus, it is preferable to form a transistor having a structure appropriate for characteristics of each of the various circuits. For example, a transistor having an Loff region is preferably used as a pixel transistor in order to suppress the off-current value. On the other hand, as a transistor in a peripheral circuit, a transistor having an Lov region is preferably used in order to prevent deterioration in the on-current value by relieving the electric field in the vicinity of the drain.

A transistor 110104 is a transistor including a sidewall 110121 in contact with the side surface of the gate electrode 110117. When the transistor includes the sidewall 110121, a region overlapping with the sidewall 110121 can be made to be an LDD region.

A transistor 110105 is a transistor in which an LDD (Loff) region is formed by performing doping of the semiconductor layer with the use of a mask. Thus, the LDD region can surely be formed, and an off-current value of the transistor can be reduced.

A transistor 110106 is a transistor in which an LDD (Lov) region is formed by performing doping of the semiconductor layer with the use of a mask. Thus, the LDD region can surely be formed, and deterioration in an on-current value can be prevented by relieving the electric field in the vicinity of the drain of the transistor.

Next, an example of a method for manufacturing a transistor included in the display device to which the present invention can be applied is described with reference to FIGS. 56B to 56G.

Note that a structure and a manufacturing method of a transistor included in the display device to which the present invention can be applied are not limited to those in FIGS. 56A to 56G, and various structures and manufacturing methods can be used.

In this embodiment mode, a surface of the substrate 110111, a surface of the insulating film 110112, a surface of the semiconductor layer 110113, a surface of the semiconductor layer 110114, a surface of the semiconductor layer 110115, a surface of the insulating film 110116, a surface of the insulating film 110118, or a surface of the insulating film 110119 is oxidized or nitrided by using plasma treatment, so that the semiconductor layer or the insulating film can be oxidized or nitrided. By oxidizing or nitriding the semiconductor layer or the insulating film by plasma treatment in such a manner, the surface of the semiconductor layer or the insulating film is modified, and the insulating film can be formed to be denser than an insulating film formed by a CVD method or a sputtering method. Thus, a defect such as a pinhole can be suppressed, and characteristics and the like of the display device can be improved.

First, the surface of the substrate 110111 is washed using hydrofluoric acid (HF), alkaline, or pure water. The substrate 110111 can be a glass substrate using barium borosilicate glass, aluminoborosilicate glass, or the like, a quartz substrate, a ceramic substrate, a metal substrate containing stainless steel, or the like. Further, a substrate formed of plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or a substrate formed of a flexible synthetic resin such as acrylic can also be used. Here, the case where a glass substrate is used as the substrate 110111 is shown.

Here, an oxide film or a nitride film may be formed on the surface of the substrate 110111 by oxidizing or nitriding the surface of the substrate 110111 by plasma treatment (FIG. 56B). Hereinafter, an insulating film such as an oxide film or a nitride film formed by performing plasma treatment on the surface is also referred to as a plasma-treated insulating film. In FIG. 56B, an insulating film 110131 is a plasma-treated insulating film. In general, when a semiconductor element such as a thin film transistor is provided over a substrate formed of glass, plastic, or the like, an impurity element such as alkali metal (e.g., Na) or alkaline earth metal included in glass, plastic, or the like might be mixed into the semiconductor element so that the semiconductor element is contaminated; thus, characteristics of the semiconductor element may be adversely affected in some cases. Nitridation of a surface of the substrate formed of glass, plastic, or the like can prevent an impurity element such as alkali metal (e.g., Na) or alkaline earth metal included in the substrate from being mixed into the semiconductor element.

When the surface is oxidized by plasma treatment, the plasma treatment is performed in an oxygen atmosphere (e.g., in an atmosphere of oxygen (O₂) and a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe), in an atmosphere of oxygen, hydrogen (H₂), and a rare gas, or in an atmosphere of dinitrogen monoxide and a rare gas). On the other hand, when the surface is nitrided by plasma treatment, the plasma treatment is performed in a nitrogen atmosphere (e.g., in an atmosphere of nitrogen (N₂) and a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe), in an atmosphere of nitrogen, hydrogen, and a rare gas, or in an atmosphere of NH₃ and a rare gas). As a rare gas, Ar can be used, for example. Alternatively, a gas in which Ar and Kr are mixed may be used. Accordingly, the plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. For example, the plasma-treated insulating film contains Ar when Ar is used.

In addition, it is preferable to perform plasma treatment in the atmosphere containing the aforementioned gas, with conditions of an electron density in the range of 1×10¹¹ to 1×10¹³ cm⁻³ and a plasma electron temperature in the range of 0.5 to 1.5 eV. Since the plasma electron density is high and the electron temperature in the vicinity of an object to be treated is low, damage by plasma to the object to be treated can be prevented. Further, since the plasma electron density is as high as 1×10¹¹ cm³ or more, an oxide film or a nitride film formed by oxidizing or nitriding the object to be treated by plasma treatment is superior in its uniformity of thickness and the like as well as being dense, as compared with a film formed by a CVD method, a sputtering method, or the like. Alternatively, since the plasma electron temperature is as low as 1 eV or less, oxidation or nitridation can be performed at a lower temperature as compared with a conventional plasma treatment or thermal oxidation. For example, oxidation or nitridation can be performed sufficiently even when plasma treatment is performed at a temperature lower than a strain point of a glass substrate by 100 degrees or more. Note that as frequency for generating plasma, high frequency waves such as microwaves (2.45 GHz) can be used. Note that hereinafter, plasma treatment is performed using the aforementioned conditions unless otherwise specified.

Note that although FIG. 56B shows the case where the plasma-treated insulating film is formed by plasma treatment on the surface of the substrate 110111, this embodiment mode includes the case where a plasma-treated insulating film is not formed on the surface of the substrate 110111.

Note that although a plasma-treated insulating film formed by plasma treatment on the surface of the object to be treated is not shown in FIGS. 56C to 56G, this embodiment mode includes the case where a plasma-treated insulating film formed by plasma treatment exists on the surface of the substrate 110111, the insulating film 110112, the semiconductor layer 110113, the semiconductor layer 110114, the semiconductor layer 110115, the insulating film 110116, the insulating film 110118, or the insulating film 110119.

Next, the insulating film 110112 is formed over the substrate 110111 by a known method (such as a sputtering method, an LPCVD method, or a plasma CVD method) (FIG. 56C). For the insulating film 110112, silicon oxide (SiO_(x)) or silicon oxynitride (SiO_(x)N_(y)) (x>y) can be used.

Here, a plasma-treated insulating film may be formed on the surface of the insulating film 110112 by oxidizing or nitriding the surface of the insulating film 110112 by plasma treatment. By oxidizing the surface of the insulating film 110112, the surface of the insulating film 110112 is modified, and a dense film with fewer defects such as a pinhole can be obtained. Further, by oxidizing the surface of the insulating film 110112, the plasma-treated insulating film containing a little amount of N atoms can be formed; thus, interface characteristics of the plasma-treated insulating film and a semiconductor layer are improved when the semiconductor layer is provided over the plasma-treated insulating film. The plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. Note that the plasma treatment can be similarly performed under the aforementioned conditions.

Next, the island-shaped semiconductor layers 110113 and 110114 are formed over the insulating film 110112 (FIG. 56D). The island-shaped semiconductor layers 110113 and 110114 can be formed in such a manner that an amorphous semiconductor layer is formed over the insulating film 110112 by using a material containing silicon (Si) as its main component (e.g., Si_(x)Ge_(1-x)) or the like by a known method (such as a sputtering method, an LPCVD method, or a plasma CVD method), the amorphous semiconductor layer is crystallized, and the semiconductor layer is selectively etched. Note that crystallization of the amorphous semiconductor layer can be performed by a known crystallization method such as a laser crystallization method, a thermal crystallization method using RTA or an annealing furnace, a thermal crystallization method using a metal element which promotes crystallization, or a method in which these methods are combined. Here, end portions of the island-shaped semiconductor layers are provided with an angle of about 90° (θ=85 to 100°). Alternatively, the semiconductor layer 110114 to be a low concentration drain region may be formed by doping impurities with the use of a mask.

Here, a plasma-treated insulating film may be formed on the surfaces of the semiconductor layers 110113 and 110114 by oxidizing or nitriding the surfaces of the semiconductor layers 110113 and 110114 by plasma treatment. For example, when Si is used for the semiconductor layers 110113 and 110114, silicon oxide (SiO_(x)) or silicon nitride (SiN_(x)) is formed as the plasma-treated insulating film. Alternatively, after being oxidized by plasma treatment, the semiconductor layers 110113 and 110114 may be nitrided by performing plasma treatment again. In this case, silicon oxide (SiO_(x)) is formed in contact with the semiconductor layers 110113 and 110114, and silicon nitride oxide (SiN_(x)O_(y)) (x>y) is formed on the surface of the silicon oxide. Note that when the semiconductor layer is oxidized by plasma treatment, the plasma treatment is performed in an oxygen atmosphere (e.g., in an atmosphere of oxygen (O₂) and a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe), in an atmosphere of oxygen, hydrogen (H₂), and a rare gas, or in an atmosphere of dinitrogen monoxide and a rare gas). On the other hand, when the semiconductor layer is nitrided by plasma treatment, the plasma treatment is performed in a nitrogen atmosphere (e.g., in an atmosphere of nitrogen (N₂) and a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe), in an atmosphere of nitrogen, hydrogen, and a rare gas, or in an atmosphere of NH₃ and a rare gas). As a rare gas, Ar can be used, for example. Alternatively, a gas in which Ar and Kr are mixed may be used. Accordingly, the plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. For example, the plasma-treated insulating film contains Ar when Ar is used.

Next, the insulating film 110116 is formed (FIG. 56E). The insulating film 110116 can have a single-layer structure or a stacked-layer structure of an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y), by a known method (such as a sputtering method, an LPCVD method, or a plasma CVD method). Note that when the plasma-treated insulating film is formed on the surfaces of the semiconductor layers 110113 and 110114 by performing plasma treatment on the surfaces of the semiconductor layers 110113 and 110114, the plasma-treated insulating film can be used as the insulating film 110116.

Here, the surface of the insulating film 110116 may be oxidized or nitrided by plasma treatment, so that a plasma-treated insulating film is formed on the surface of the insulating film 110116. Note that the plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. The plasma treatment can be similarly performed under the aforementioned conditions.

Alternatively, after the insulating film 110116 is oxidized by performing plasma treatment once in an oxygen atmosphere, the insulating film 110116 may be nitrided by performing plasma treatment again in a nitrogen atmosphere. By oxidizing or nitriding the surface of the insulating film 110116 by plasma treatment in such a manner, the surface of the insulating film 110116 is modified, and a dense film can be formed. An insulating film obtained by plasma treatment is denser and has fewer defects such as a pinhole, as compared with an insulating film formed by a CVD method, a sputtering method, or the like. Thus, characteristics of a thin film transistor can be improved.

Next, the gate electrode 110117 is formed (FIG. 56F). The gate electrode 110117 can be formed by a known method (such as a sputtering method, an LPCVD method, or a plasma CVD method).

In the transistor 110101, the semiconductor layers 110115 used as the source region and the drain region can be formed by doping impurities after the gate electrode 110117 is formed.

In the transistor 110102, the semiconductor layers 110114 used as the LDD regions and the semiconductor layers 110115 used as the source region and the drain region can be formed by doping impurities after the gate electrode 110117 is formed.

In the transistor 110103, the semiconductor layers 110114 used as the LDD regions and the semiconductor layers 110115 used as the source region and the drain region can be formed by doping impurities after the gate electrode 110117 is formed.

In the transistor 110104, the semiconductor layers 110114 used as the LDD regions and the semiconductor layers 110115 used as the source region and the drain region can be formed by doping impurities after the sidewall 110121 is formed on the side surface of the gate electrode 110117.

Note that silicon oxide (SiO_(x)) or silicon nitride (SiN_(x)) can be used for the sidewall 110121. As a method of forming the sidewall 110121 on the side surface of the gate electrode 110117, a method can be used, for example, in which a silicon oxide (SiO_(x)) film or a silicon nitride (SiN_(x)) film is formed by a known method after the gate electrode 110117 is formed, and then, the silicon oxide (SiO_(x)) film or the silicon nitride (SiN_(x)) film is etched by anisotropic etching. Thus, the silicon oxide (SiO_(x)) film or the silicon nitride (SiN_(x)) film remains only on the side surface of the gate electrode 110117, so that the sidewall 110121 can be formed on the side surface of the gate electrode 110117.

In the transistor 110105, the semiconductor layers 110114 used as the LDD (Loff) regions and the semiconductor layer 110115 used as the source region and the drain region can be formed by doping impurities after a mask 110122 is formed to cover the gate electrode 110117.

In the transistor 110106, the semiconductor layers 110114 used as the LDD (Lov) regions and the semiconductor layers 110115 used as the source region and the drain region can be formed by doping impurities after the gate electrode 110117 is formed.

Next, the insulating film 110118 is formed (FIG. 56G). The insulating film 110118 can have a single-layer structure or a stacked-layer structure of an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y); or a film containing carbon, such as a DLC (diamond-like carbon), by a known method (such as a sputtering method or a plasma CVD method).

Here, the surface of the insulating film 110118 may be oxidized or nitrided by plasma treatment, so that a plasma-treated insulating film is formed on the surface of the insulating film 110118. Note that the plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. The plasma treatment can be similarly performed under the aforementioned conditions.

Next, the insulating film 110119 is formed. The insulating film 110119 can have a single-layer structure or a stacked-layer structure of an organic material such as epoxy, polyimide, polyamide, polyvinyl phenol, benzocyclobutene, or acrylic; or a siloxane resin, in addition to an insulating film containing oxygen or nitrogen, such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y)) (x>y), or silicon nitride oxide (SiN_(x)O_(y)) (x>y); or a film containing carbon, such as a DLC (diamond-like carbon), by known method (such as a sputtering method or a plasma CVD method). Note that a siloxane resin corresponds to a resin having Si—O—Si bonds. Siloxane includes a skeleton structure of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used. Alternatively, a fluoro group, or a fluoro group and an organic group containing at least hydrogen can be used as a substituent. In addition, the plasma-treated insulating film contains a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe) used for the plasma treatment. For example, the plasma-treated insulating film contains Ar when Ar is used.

When an organic material such as polyimide, polyamide, polyvinyl phenol, benzocyclobutene, or acrylic, or a siloxane resin is used for the insulating film 110119, the surface of the insulating film 110119 can be modified by oxidizing or nitriding the surface of the insulating film by plasma treatment. Modification of the surface improves strength of the insulating film 110119, and physical damage such as a crack generated when an opening is formed, for example, or film reduction in etching can be reduced. Further, when the conductive film 110123 is formed over the insulating film 110119, modification of the surface of the insulating film 110119 improves adhesion to the conductive film. For example, when a siloxane resin is used for the insulating film 110119 and nitrided by plasma treatment, a plasma-treated insulating film containing nitrogen or a rare gas is formed by nitriding a surface of the siloxane resin, and physical strength is improved.

Next, a contact hole is formed in the insulating films 110119, 110118, and 110116 in order to form the conductive film 110123 which is electrically connected to the semiconductor layer 110115. Note that the contact hole may have a tapered shape. Thus, coverage with the conductive film 110123 can be improved.

FIG. 60 shows cross-sectional structures of a bottom-gate transistor and a capacitor.

A first insulating film (an insulating film 110502) is formed over an entire surface of a substrate 110501. The first insulating film can prevent impurities from the substrate from adversely affecting a semiconductor layer and changing properties of a transistor. That is, the first insulating film functions as a base film. Thus, a transistor with high reliability can be formed. As the first insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

A first conductive layer (conductive layers 110503 and 110504) is formed over the first insulating film. The conductive layer 110503 includes a portion functioning as a gate electrode of a transistor 110520. The conductive layer 110504 includes a portion functioning as a first electrode of a capacitor 110521. As the first conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

A second insulating film (an insulating film 110522) is formed to cover at least the first conductive layer. The second insulating film functions as a gate insulating film. As the second insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that for a portion of the second insulating film, which is in contact with the semiconductor layer, a silicon oxide film is preferably used. This is because the trap level at the interface between the semiconductor layer and the second insulating film is lowered.

When the second insulating film is in contact with Mo, a silicon oxide film is preferably used for a portion of the second insulating film in contact with Mo. This is because the silicon oxide film does not oxidize Mo.

A semiconductor layer is formed in part of a portion over the second insulating film, which overlaps with the first conductive layer, by a photolithography method, an inkjet method, a printing method, or the like. Part of the semiconductor layer extends to a portion over the second insulating film, which does not overlap with the first conductive layer. The semiconductor layer includes a channel formation region (a channel formation region 110510), an LDD region (LDD regions 110508 and 110509), and an impurity region (impurity regions 110505, 110506, and 110507). The channel formation region 110510 functions as a channel formation region of the transistor 110520. The LDD regions 110508 and 110509 function as LDD regions of the transistor 110520. Note that the LDD regions 110508 and 110509 are not necessarily formed. The impurity region 110505 includes a portion functioning as one of a source electrode and a drain electrode of the transistor 110520. The impurity region 110506 includes a portion functioning as the other of the source electrode and the drain electrode of the transistor 110520. The impurity region 110507 includes a portion functioning as a second electrode of the capacitor 110521.

A third insulating film (an insulating film 110511) is entirely formed. A contact hole is selectively formed in part of the third insulating film. The insulating film 110511 functions as an interlayer film. As the third insulating film, an inorganic material (e.g., silicon oxide, silicon nitride, or silicon oxynitride), an organic compound material having a low dielectric constant (e.g., a photosensitive or nonphotosensitive organic resin material), or the like can be used. Alternatively, a material containing siloxane may be used. Note that siloxane is a material in which a skeleton structure is formed by a bond of silicon (Si) and oxygen (O). As a substitute, an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used. Alternatively, a fluoro group, or a fluoro group and an organic group containing at least hydrogen may be used as a substituent.

A second conductive layer (conductive layers 110512 and 110513) is formed over the third insulating film. The conductive layer 110512 is connected to the other of the source electrode and the drain electrode of the transistor 110520 through the contact hole formed in the third insulating film. Thus, the conductive layer 110512 includes a portion functioning as the other of the source electrode and the drain electrode of the transistor 110520. The conductive layer 110513 includes a portion functioning as the first electrode of the capacitor 110521. As the second conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

Note that in steps after forming the second conductive layer, various insulating films or various conductive films may be formed.

Next, structures of a transistor and a capacitor are described in the case where an amorphous silicon (a-Si:H) film is used as a semiconductor layer of the transistor.

FIG. 57 shows cross-sectional structures of a top-gate transistor and a capacitor.

A first insulating film (an insulating film 110202) is formed over an entire surface of a substrate 110201. The first insulating film can prevent impurities from the substrate from adversely affecting a semiconductor layer and changing properties of a transistor. That is, the first insulating film functions as a base film. Thus, a transistor with high reliability can be formed. As the first insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that the first insulating film is not necessarily formed. When the first insulating film is not formed, reduction in the number of steps and reduction in manufacturing cost can be realized. Further, since the structure can be simplified, the yield can be improved.

A first conductive layer (conductive layers 110203, 110204, and 110205) is formed over the first insulating film. The conductive layer 110203 includes a portion functioning as one of a source electrode and a drain electrode of a transistor 110220. The conductive layer 110204 includes a portion functioning as the other of the source electrode and the drain electrode of the transistor 110220. The conductive layer 110205 includes a portion functioning as a first electrode of a capacitor 110221. As the first conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

A first semiconductor layer (semiconductor layers 110206 and 110207) is formed above the conductive layers 110203 and 110204. The semiconductor layer 110206 includes a portion functioning as one of the source electrode and the drain electrode. The semiconductor layer 110207 includes a portion functioning as the other of the source electrode and the drain electrode. As the first semiconductor layer, silicon containing phosphorus or the like can be used, for example.

A second semiconductor layer (a semiconductor layer 110208) is formed over the first insulating film and between the conductive layer 110203 and the conductive layer 110204. Part of the semiconductor layer 110208 extends over the conductive layers 110203 and 110204. The semiconductor layer 110208 includes a portion functioning as a channel formation region of the transistor 110220. As the second semiconductor layer, a semiconductor layer having no crystallinity such as an amorphous silicon (a-Si:H) layer, a semiconductor layer such as a microcrystalline semiconductor (μ-Si:H) layer, or the like can be used.

A second insulating film (insulating films 110209 and 110210) is formed to cover at least the semiconductor layer 110208 and the conductive layer 110205. The second insulating film functions as a gate insulating film. As the second insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that for a portion of the second insulating film, which is in contact with the second semiconductor layer, a silicon oxide film is preferably used. This is because the trap level at the interface between the second semiconductor layer and the second insulating film is lowered.

When the second insulating film is in contact with Mo, a silicon oxide film is preferably used for a portion of the second insulating film in contact with Mo. This is because the silicon oxide film does not oxidize Mo.

A second conductive layer (conductive layers 110211 and 110212) is formed over the second insulating film. The conductive layer 110211 includes a portion functioning as a gate electrode of the transistor 110220. The conductive layer 110212 functions as a second electrode of the capacitor 110221 or a wiring. As the second conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

Note that in steps after forming the second conductive layer, various insulating films or various conductive films may be formed.

FIG. 58 shows cross-sectional structures of an inversely staggered (bottom gate) transistor and a capacitor. In particular, the transistor shown in FIG. 58 has a channel-etched structure.

A first insulating film (an insulating film 110302) is formed over an entire surface of a substrate 110301. The first insulating film can prevent impurities from the substrate from adversely affecting a semiconductor layer and changing properties of a transistor. That is, the first insulating film functions as a base film. Thus, a transistor with high reliability can be formed. As the first insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that the first insulating film is not necessarily formed. When the first insulating film is not formed, reduction in the number of steps and reduction in manufacturing cost can be realized. Further, since the structure can be simplified, the yield can be improved.

A first conductive layer (conductive layers 110303 and 110304) is formed over the first insulating film. The conductive layer 110303 includes a portion functioning as a gate electrode of a transistor 110320. The conductive layer 110304 includes a portion functioning as a first electrode of a capacitor 110321. As the first conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

A second insulating film (an insulating film 110305) is formed to cover at least the first conductive layer. The second insulating film functions as a gate insulating film. As the second insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that for a portion of the second insulating film, which is in contact with the semiconductor layer, a silicon oxide film is preferably used. This is because the trap level at the interface between the semiconductor layer and the second insulating film is lowered.

When the second insulating film is in contact with Mo, a silicon oxide film is preferably used for a portion of the second insulating film in contact with Mo. This is because the silicon oxide film does not oxidize Mo.

A first semiconductor layer (a semiconductor layer 110306) is formed in part of a portion over the second insulating film, which overlaps with the first conductive layer, by a photolithography method, an inkjet method, a printing method, or the like. Part of the semiconductor layer 110306 extends to a portion over the second insulating film, which does not overlap with the first conductive layer. The semiconductor layer 110306 includes a portion functioning as a channel formation region of the transistor 110320. As the semiconductor layer 110306, a semiconductor layer having no crystallinity such as an amorphous silicon (a-Si:H) layer, a semiconductor layer such as a microcrystalline semiconductor (μ-Si:H) layer, or the like can be used.

A second semiconductor layer (semiconductor layers 110307 and 110308) is formed over part of the first semiconductor layer. The semiconductor layer 110307 includes a portion functioning as one of a source electrode and a drain electrode. The semiconductor layer 110308 includes a portion functioning as the other of the source electrode and the drain electrode. As the second semiconductor layer, silicon containing phosphorus or the like can be used, for example.

A second conductive layer (conductive layers 110309, 110310, and 110311) is formed over the second semiconductor layer and the second insulating film. The conductive layer 110309 includes a portion functioning as one of the source electrode and the drain electrode of the transistor 110320. The conductive layer 110310 includes a portion functioning as the other of the source electrode and the drain electrode of the transistor 110320. The conductive layer 110311 includes a portion functioning as a second electrode of the capacitor 110321. As the second conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternatively, a stacked layer of these elements (including the alloy thereof) can be used.

Note that in steps after forming the second conductive layer, various insulating films or various conductive films may be formed.

Here, an example of a step which is characteristic of the channel-etched type transistor is described. The first semiconductor layer and the second semiconductor layer can be formed using the same mask. Specifically, the first semiconductor layer and the second semiconductor layer are continuously formed. Further, the first semiconductor layer and the second semiconductor layer are formed using the same mask.

Another example of a step which is characteristic of the channel-etched type transistor is described. The channel formation region of the transistor can be formed without using an additional mask. Specifically, after the second conductive layer is formed, part of the second semiconductor layer is removed using the second conductive layer as a mask. Alternatively, part of the second semiconductor layer is removed by using the same mask as the second conductive layer. The first semiconductor layer below the removed second semiconductor layer serves as the channel formation region of the transistor.

FIG. 59 shows cross-sectional structures of an inversely staggered (bottom gate) transistor and a capacitor. In particular, the transistor shown in FIG. 59 has a channel protection (channel stop) structure.

A first insulating film (an insulating film 110402) is formed over an entire surface of a substrate 110401. The first insulating film can prevent impurities from the substrate from adversely affecting a semiconductor layer and changing properties of a transistor. That is, the first insulating film functions as a base film. Thus, a transistor with high reliability can be formed. As the first insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that the first insulating film is not necessarily formed. When the first insulating film is not formed, reduction in the number of steps and reduction in manufacturing cost can be realized. Further, since the structure can be simplified, the yield can be improved.

A first conductive layer (conductive layers 110403 and 110404) is formed over the first insulating film. The conductive layer 110403 includes a portion functioning as a gate electrode of a transistor 110420. The conductive layer 110404 includes a portion functioning as a first electrode of a capacitor 110421. As the first conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternately, a stacked layer of these elements (including the alloy thereof) can be used.

A second insulating film (an insulating film 110405) is formed to cover at least the first conductive layer. The second insulating film functions as a gate insulating film. As the second insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

Note that for a portion of the second insulating film, which is in contact with the semiconductor layer, a silicon oxide film is preferably used. This is because the trap level at the interface between the semiconductor layer and the second insulating film is lowered.

When the second insulating film is in contact with Mo, a silicon oxide film is preferably used for a portion of the second insulating film in contact with Mo. This is because the silicon oxide film does not oxidize Mo.

A first semiconductor layer (a semiconductor layer 110406) is formed in part of a portion over the second insulating film, which overlaps with the first conductive layer, by a photolithography method, an inkjet method, a printing method, or the like. Part of the semiconductor layer 110406 extends to a portion over the second insulating film, which does not overlap with the first conductive layer. The semiconductor layer 110406 includes a portion functioning as a channel formation region of the transistor 110420. As the semiconductor layer 110406, a semiconductor layer having no crystallinity such as an amorphous silicon (a-Si:H) layer, a semiconductor layer such as a microcrystalline semiconductor (μ-Si:H) layer, or the like can be used.

A third insulating film (an insulating film 110412) is formed over part of the first semiconductor layer. The insulating film 110412 prevents the channel formation region of the transistor 110420 from being removed by etching. That is, the insulating film 110412 functions as a channel protection film (a channel stop film). As the third insulating film, a single layer or a stacked layer of a silicon oxide film, a silicon nitride film, a silicon oxynitride film (SiO_(x)N_(y)), or the like can be used.

A second semiconductor layer (semiconductor layers 110407 and 110408) is formed over part of the first semiconductor layer and part of the third insulating film. The semiconductor layer 110407 includes a portion functioning as one of a source electrode and a drain electrode. The semiconductor layer 110408 includes a portion functioning as the other of the source electrode and the drain electrode. As the second semiconductor layer, silicon containing phosphorus or the like can be used, for example.

A second conductive layer (conductive layers 110409, 110410, and 110411) is formed over the second semiconductor layer. The conductive layer 110409 includes a portion functioning as one of the source electrode and the drain electrode of the transistor 110420. The conductive layer 110410 includes a portion functioning as the other of the source electrode and the drain electrode of the transistor 110420. The conductive layer 110411 includes a portion functioning as a second electrode of the capacitor 110421. As the second conductive layer, an element such as Ti, Mo, Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, or Ge, or an alloy of these elements can be used. Alternately, a stacked layer of these elements (including the alloy thereof) can be used.

Note that in steps after forming the second conductive layer, various insulating films or various conductive films may be formed.

Here, an example of a step which is characteristic of the channel protection type transistor is described. The first semiconductor layer, the second semiconductor layer, and the second conductive layer can be formed using the same mask. At the same time, the channel formation region can be formed. Specifically, the first semiconductor layer is formed, and then, the third insulating film (i.e., the channel protection film or the channel stop film) is patterned using a mask. Next, the second semiconductor layer and the second conductive layer are continuously formed. Then, after the second conductive layer is formed, the first semiconductor layer, the second semiconductor layer, and the second conductive film are patterned using the same mask. Note that part of the first semiconductor layer below the third insulating film is protected by the third insulating film, and thus is not removed by etching. This part (a part of the first semiconductor layer over which the third insulating film is formed) serves as the channel formation region.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 13

In this embodiment mode, a structure of an EL element is described. In particular, a structure of an inorganic EL element is described.

An inorganic EL element is classified as either a dispersion type inorganic EL element or a thin-film type inorganic EL element, depending on its element structure. These elements differ in that the former includes an electroluminescent layer in which particles of a light-emitting material are dispersed in a binder, whereas the latter includes an electroluminescent layer formed of a thin film of a light-emitting material. However, the former and the latter have in common in that they need electrons accelerated by a high electric field. Note that mechanisms for obtaining light emission are donor-acceptor recombination light emission which utilizes a donor level and an acceptor level; and localized light emission which utilizes inner-shell electron transition of a metal ion. In general, donor-acceptor recombination light emission is employed in dispersion type inorganic EL elements and localized light emission is employed in thin-film type inorganic EL elements in many cases.

A light-emitting material includes a base material and an impurity element to be a luminescence center. Light emission of various colors can be obtained by changing the impurity element to be included. The light-emitting material can be formed using various methods, such as a solid phase method or a liquid phase method (a coprecipitation method). Further, a liquid phase method such as a spray pyrolysis method, a double decomposition method, a method employing precursor pyrolysis, a reverse micelle method, a method in which one or more of these methods are combined with high-temperature baking, or a freeze-drying method, or the like can be used.

A solid phase method is a method in which a base material and an impurity element or a compound containing an impurity element are weighed, mixed in a mortar, and heated and baked in an electric furnace so as to be reacted; thus, the impurity element is included in the base material. The baking temperature is preferably 700 to 1500° C. This is because a solid-phase reaction does not proceed when the temperature is too low, and the base material decomposes when the temperature is too high. Note that although the materials may be baked in powder form, they are preferably baked in pellet form. Although a solid phase method needs a comparatively high temperature, it is a simple method, and thus has high productivity and is suitable for mass production.

A liquid phase method (a coprecipitation method) is a method in which a base material or a compound containing a base material, and an impurity element or a compound containing an impurity element are reacted in a solution, dried, and then baked. Particles of a light-emitting material are uniformly distributed, and the reaction can progress even when the particles are small and the baking temperature is low.

As a base material to be used for a light-emitting material, sulfide, oxide, or nitride can be used. As sulfide, zinc sulfide (ZnS), cadmium sulfide (CdS), calcium sulfide (CaS), yttrium sulfide (Y₂S₃), gallium sulfide (Ga₂S₃), strontium sulfide (SrS), barium sulfide (BaS), or the like can be used, for example. As oxide, zinc oxide (ZnO), yttrium oxide (Y₂O₃), or the like can be used, for example. As nitride, aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), or the like can be used, for example. Further, zinc selenide (ZnSe), zinc telluride (ZnTe), or the like; or a ternary mixed crystal such as calcium gallium sulfide (CaGa₂S₄), strontium gallium sulfide (SrGa₂S₄), or barium gallium sulfide (BaGa₂S₄) may be used.

As a luminescence center for localized light emission, manganese (Mn), copper (Cu), samarium (Sm), terbium (Th), erbium (Er), thulium (Tm), europium (Eu), cerium (Ce), praseodymium (Pr), or the like can be used. Note that a halogen element such as fluorine (F) or chlorine (Cl) may be added for charge compensation.

On the other hand, as a luminescence center for donor-acceptor recombination light emission, a light-emitting material including a first impurity element forming a donor level and a second impurity element forming an acceptor level can be used. As the first impurity element, fluorine (F), chlorine (Cl), aluminum (Al), or the like can be used, for example. As the second impurity element, copper (Cu), silver (Ag), or the like can be used, for example.

When the light-emitting material for donor-acceptor recombination light emission is synthesized by a solid phase method, a base material, the first impurity element or a compound containing the first impurity element, and the second impurity element or a compound containing the second impurity element are weighed, mixed in a mortar, and heated and baked in an electric furnace. As the base material, the aforementioned base material can be used. As the first impurity element or the compound containing the first impurity element, fluorine (F), chlorine (Cl), aluminum sulfide (Al₂S₃), or the like can be used, for example. As the second impurity element or the compound containing the second impurity element, copper (Cu), silver (Ag), copper sulfide (Cu₂S), silver sulfide (Ag₂S), or the like can be used, for example. The baking temperature is preferably 700 to 1500° C. This is because a solid-phase reaction does not proceed when the temperature is too low, and the base material decomposes when the temperature is too high. Note that although the materials may be baked in powder form, they are preferably baked in pellet form.

As the impurity element in the case of using a solid phase reaction, compounds including the first impurity element and the second impurity element may be used in combination. In this case, the impurity elements are easily diffused, and the solid phase reaction proceeds readily, so that a uniform light-emitting material can be obtained. Further, since an unnecessary impurity element is not included, a light-emitting material with high purity can be obtained. As the compound including the first impurity element and the second impurity element, copper chloride (CuCl), silver chloride (AgCl), or the like can be used, for example.

Note that the concentration of these impurity elements is in the range of 0.01 to 10 atomic percent, and is preferably in the range of 0.05 to 5 atomic percent with respect to the base material.

In the case of a thin-film type inorganic EL element, an electroluminescent layer includes the aforementioned light-emitting material, and can be formed using a physical vapor deposition (PVD) method such as a sputtering method or a vacuum evaporation method, for example, a resistance heating evaporation method or an electron beam evaporation (EB evaporation) method, a chemical vapor deposition (CVD) method such as a metal organic CVD method or a low-pressure hydride transport CVD method, an atomic layer epitaxy (ALE) method, or the like.

FIGS. 61A to 61C each show an example of a thin-film type inorganic EL element which can be used as the light-emitting element. In FIGS. 61A to 61C, a light-emitting element includes a first electrode layer 120100, an electroluminescent layer 120102, and a second electrode layer 120103.

The light-emitting elements shown in FIGS. 61B and 61C each have a structure where an insulating film is provided between the electrode layer and the electroluminescent layer in the light-emitting element in FIG. 61A. The light-emitting element shown in FIG. 61B includes an insulating film 120104 between the first electrode layer 120100 and the electroluminescent layer 120102. The light-emitting element shown in FIG. 61C includes an insulating film 120105 between the first electrode layer 120100 and the electroluminescent layer 120102, and an insulating film 120106 between the second electrode layer 120103 and the electroluminescent layer 120102.

In such a manner, the insulating film may be provided between the electroluminescent layer and one of the electrode layers interposing the electroluminescent layer, or may be provided between the electroluminescent layer and each of the electrode layers interposing the electroluminescent layer. The insulating film may be a single layer or stacked layers including a plurality of layers.

Note that the insulating film 120104 is provided in contact with the first electrode layer 120100 in FIG. 61B; however, the insulating film 120104 may be provided in contact with the second electrode layer 120103 by reversing the order of the insulating film and the electroluminescent layer.

In the case of a dispersion type inorganic EL, a film-shaped electroluminescent layer is formed by dispersing particulate light-emitting materials in a binder. When particles with a desired size cannot be sufficiently obtained by a method of forming the light-emitting material, the light-emitting materials may be processed into particles by being crushed in a mortar or the like. The binder is a substance for fixing the particulate light-emitting material in a dispersed state and maintaining the shape as the electroluminescent layer. The light-emitting material is uniformly dispersed in the electroluminescent layer and fixed by the binder.

In the case of a dispersion type inorganic EL, as a method of forming the electroluminescent layer, a droplet discharging method by which the electroluminescent layer can be selectively formed, a printing method (such as screen printing or offset printing), a coating method such as a spin coating method, a dipping method, a dispenser method, or the like can be used. The thickness of the electroluminescent layer is not particularly limited, but preferably in the range of 10 to 1000 nm. In the electroluminescent layer including the light-emitting material and the binder, a ratio of the light-emitting material is preferably 50 wt % or more and 80 wt % or less.

FIGS. 62A to 62C each show an example of a dispersion type inorganic EL element which can be used as the light-emitting element. A light-emitting element in FIG. 62A has a stacked-layer structure of a first electrode layer 120200, an electroluminescent layer 120202, and a second electrode layer 120203. The electroluminescent layer 120202 includes a light-emitting material 120201 held by a binder.

An insulating material can be used for the binder. As the insulating material, an organic material or an inorganic material can be used. Alternatively, a mixed material containing an organic material and an inorganic material may be used. As the organic insulating material, a polymer having a comparatively high dielectric constant, such as a cyanoethyl cellulose based resin, or a resin such as polyethylene, polypropylene, a polystyrene based resin, a silicone resin, an epoxy resin, or vinylidene fluoride can be used. Alternatively, a heat-resistant polymer such as aromatic polyamide or polybenzimidazole, or a siloxane resin may be used. Note that a siloxane resin corresponds to a resin having Si—O—Si bonds. Siloxane includes a skeleton structure of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used. Alternatively, a fluoro group, or a fluoro group and an organic group containing at least hydrogen may be used as a substituent. Further alternately, a resin material, for example, a vinyl resin such as polyvinyl alcohol or polyvinylbutyral, a phenol resin, a novolac resin, an acrylic resin, a melamine resin, an urethane resin, or an oxazole resin (polybenzoxazole) may be used. A dielectric constant can be adjusted by appropriately mixing these resins with fine particles having a high dielectric constant, such as barium titanate (BaTiO₃) or strontium titanate (SrTiO₃).

The inorganic insulating material included in the binder can be formed using silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon containing oxygen and nitrogen, aluminum nitride (AlN), aluminum containing oxygen and nitrogen, aluminum oxide (Al₂O₃) containing oxygen and nitrogen, titanium oxide (TiO₂), BaTiO₃, SrTiO₃, lead titanate (PbTiO₃), potassium niobate (KNbO₃), lead niobate (PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalite (BaTa₂O₆), lithium tantalite (LiTaO₃), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂), ZnS, or a substance containing another inorganic insulating material. When an inorganic material having a high dielectric constant is included in the organic material (by addition or the like), the dielectric constant of the electroluminescent layer formed of the light-emitting material and the binder can be more effectively controlled, and the dielectric constant can be further increased.

In a manufacturing step, the light-emitting material is dispersed in a solution containing the binder. As a solvent for the solution containing the binder, it is acceptable as long as a solvent dissolves a binder material and can make a solution having a viscosity suitable for a method of forming the electroluminescent layer (various wet processes) and for desired film thickness. For example, an organic solvent or the like can be used as the solvent. When a siloxane resin is used as the binder, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate (also referred to as PGMEA), 3-methoxy-3-methyl-1-butanol (also referred to as MMB), or the like can be used as the solvent.

The light-emitting elements shown in FIGS. 62B and 62C each have a structure where an insulating film is provided between the electrode layer and the electroluminescent layer in the light-emitting element in FIG. 62A. The light-emitting element shown in FIG. 62B includes an insulating film 120204 between the first electrode layer 120200 and the electroluminescent layer 120202. The light-emitting element shown in FIG. 62C includes an insulating film 120205 between the first electrode layer 120200 and the electroluminescent layer 120202, and an insulating film 120206 between the second electrode layer 120203 and the electroluminescent layer 120202. In such a manner, the insulating film may be provided between the electroluminescent layer and one of the electrode layers interposing the electroluminescent layer, or may be provided between the electroluminescent layer and each of the electrode layers interposing the electroluminescent layer. The insulating film may be a single layer or stacked layers including a plurality of layers.

Although the insulating film 120204 is provided in contact with the first electrode layer 120200 in FIG. 62B, the insulating film 120204 may be provided in contact with the second electrode layer 120203 by reversing the order of the insulating film and the electroluminescent layer.

A material used for an insulating film such as the insulating film 120104 in FIG. 61B and the insulating film 120204 in FIG. 62B preferably has high withstand voltage and dense film quality. Further, the material preferably has a high dielectric constant. For example, silicon oxide (SiO₂), yttrium oxide (Y₂O₃), titanium oxide (TiO₂), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅), barium titanate (BaTiO₃), strontium titanate (SrTiO₃), lead titanate (PbTiO₃), silicon nitride (Si₃N₄), zirconium oxide (ZrO₂), or the like; or a mixed film of these materials or a stacked-layer film including two or more of those materials can be used. The insulating film can be formed by sputtering, evaporation, CVD, or the like. The insulating film may be formed by dispersing particles of the insulating material in a binder. A binder material may be formed using a material and a method similar to those of the binder contained in the electroluminescent layer. The thickness of the insulating film is not particularly limited, but preferably in the range of 10 to 1000 nm.

Note that the light-emitting element can emit light when voltage is applied between the pair of electrode layers interposing the electroluminescent layer. The light-emitting element can operate with DC drive or AC drive.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 14

In this embodiment mode, an example of a display device is described. In particular, the case where optical treatment is performed is described.

A rear projection display device 130100 in FIGS. 63A and 63B is provided with a projector unit 130111, a mirror 130112, and a screen panel 130101. The rear projection display device 130100 may also be provided with a speaker 130102 and operation switches 130104. The projector unit 130111 is provided at a lower portion of a housing 130110 of the rear projection display device 130100, and projects incident light which projects an image based on a video signal to the mirror 130112. The rear projection display device 130100 displays an image projected from a rear surface of the screen panel 130101.

FIG. 64 shows a front projection display device 130200. The front projection display device 130200 is provided with the projector unit 130111 and a projection optical system 130201. The projection optical system 130201 projects an image to a screen or the like provided at the front.

Hereinafter, a structure of the projector unit 130111 which is applied to the rear projection display device 130100 in FIGS. 63A and 63B and the front projection display device 130200 in FIG. 64 is described.

FIG. 65 shows a structure example of the projector unit 130111. The projector unit 130111 is provided with a light source unit 130301 and a modulation unit 130304. The light source unit 130301 is provided with a light source optical system 130303 including lenses and a light source lamp 130302. The light source lamp 130302 is stored in a housing so that stray light is not scattered. As the light source lamp 130302, a high-pressure mercury lamp or a xenon lamp, for example, which can emit a large amount of light, is used. The light source optical system 130303 is provided with an optical lens, a film having a function of polarizing light, a film for adjusting phase difference, an IR film, or the like as appropriate. The light source unit 130301 is provided so that emitted light is incident on the modulation unit 130304. The modulation unit 130304 is provided with a plurality of display panels 130308, a color filter, a dichroic mirror 130305, a total reflection mirror 130306, a prism 130309, and a projection optical system 130310. Light emitted from the light source unit 130301 is split into a plurality of optical paths by the dichroic mirror 130305.

The display panel 130308 and a color filter which transmits light with a predetermined wavelength or wavelength range are provided in each optical path. The transmissive display panel 130308 modulates transmitted light based on a video signal. Light of each color transmitted through the display panel 130308 is incident on the prism 130309, and an image is displayed on a screen through the projection optical system 130310. Note that a Fresnel lens may be provided between the mirror and the screen. Then, projected light which is projected by the projector unit 130111 and reflected by the mirror is converted into generally parallel light by the Fresnel lens and projected on the screen.

FIG. 66 shows the projector unit 130111 provided with reflective display panels 130407, 130408, and 130409.

The projector unit 130111 shown in FIG. 66 is provided with the light source unit 130301 and a modulation unit 130400. The light source unit 130301 may have a structure similar to that of FIG. 65. Light from the light source unit 130301 is split into a plurality of optical paths by dichroic mirrors 130401 and 130402 and a total reflection mirror 130403 to be incident on polarization beam splitters 130404, 130405, and 130406. The polarization beam splitters 130404, 130405, and 130406 are provided corresponding to the reflective display panels 130407, 130408, and 130409 which correspond to respective colors. The reflective display panels 130407, 130408, and 130409 modulate reflected light based on a video signal. Light of respective colors which is reflected by the reflective display panels 130407, 130408, and 130409 is incident on the prism 130109 to be synthesized, and projected through a projection optical system 130411.

Among light emitted from the light source unit 130301, only light in a wavelength region of red is transmitted through the dichroic mirror 130401 and light in wavelength regions of green and blue is reflected by the dichroic mirror 130401. Further, only the light in the wavelength region of green is reflected by the dichroic mirror 130402. The light in the wavelength region of red, which is transmitted through the dichroic mirror 130401, is reflected by the total reflection mirror 130403 and incident on the polarization beam splitter 130404. The light in the wavelength region of blue is incident on the polarization beam splitter 130405. The light in the wavelength region of green is incident on the polarization beam splitter 130406. The polarization beam splitters 130404, 130405, and 130406 have a function of splitting incident light into p-polarized light and s-polarized light and a function of transmitting only p-polarized light. The reflective display panels 130407, 130408, and 130409 polarize incident light based on a video signal.

Only s-polarized light corresponding to respective colors is incident on the reflective display panels 130407, 130408, and 130409 corresponding to respective colors. Note that the reflective display panels 130407, 130408, and 130409 may be liquid crystal panels. In this case, the liquid crystal panel operates in an electrically controlled birefringence (ECB) mode. Liquid crystal molecules are vertically aligned with respect to a substrate at a certain angle. Accordingly, in the reflective display panels 130407, 130408, and 130409, when a pixel is in an off state, display molecules are aligned so as to reflect incident light without changing a polarization state of the incident light. When the pixel is in an on state, alignment of the display molecules is changed, and the polarization state of the incident light is changed.

The projector unit 130111 in FIG. 66 can be applied to the rear projection display device 130100 in FIGS. 63A and 63B and the front projection display device 130200 in FIG. 64.

FIGS. 67A to 67C show single-panel type projector units. The projector unit 130111 shown in FIG. 67A is provided with the light source unit 130301, a display panel 130507, a projection optical system 130511, and a retardation plate 130504. The projection optical system 130511 includes one or a plurality of lenses. The display panel 130507 may be provided with a color filter.

FIG. 67B shows a structure of the projector unit 130111 operating in a field sequential mode. A field sequential mode refers to a mode in which color display is performed by light of respective colors such as red, green, and blue sequentially incident on a display panel with a time lag, without a color filter. High-definition image can be displayed particularly by combination with a display panel with high-speed response to change in input signal. In FIG. 67B, a rotating color filter plate 130505 including a plurality of color filters with red, green, blue, or the like is provided between the light source unit 130301 and a display panel 130508.

FIG. 67C shows a structure of the projector unit 130111 with a color separation method using a micro lens, as a color display method. This method refers to a method in which color display is realized by providing a micro lens array 130506 on a light incident side of a display panel 130509 and emitting light of each color from each direction. The projector unit 130111 employing this method has little loss of light due to a color filter, so that light from the light source unit 130301 can be efficiently utilized. The projector unit 130111 shown in FIG. 67C is provided with dichroic mirrors 130501, 130502, and 130503 so that light of each color is lit to the display panel 130509 from each direction.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 15

In this embodiment mode, an operation of a display device is described.

FIG. 68 shows a structure example of a display device.

A display device 180100 includes a pixel portion 180101, a signal line driver circuit 180103, and a scan line driver circuit 180104. In the pixel portion 180101, a plurality of signal lines Si to Sn extend from the signal line driver circuit 180103 in a column direction. In the pixel portion 180101, a plurality of scan lines G1 to Gm extend from the scan line driver circuit 180104 in a row direction. Pixels 180102 are arranged in matrix at each intersection of the plurality of signal lines Si to Sn and the plurality of scan lines G1 to Gm.

The signal line driver circuit 180103 has a function of outputting a signal to each of the signal lines SI to Sn. This signal may be referred to as a video signal. The scan line driver circuit 180104 has a function of outputting a signal to each of the scan lines G1 to Gm. This signal may be referred to as a scan signal.

The pixel 180102 includes at least a switching element connected to the signal line. On/off of the switching element is controlled by a potential of the scan line (a scan signal). When the switching element is turned on, the pixel 180102 is selected. On the other hand, when the switching element is turned off, the pixel 180102 is not selected.

When the pixel 180102 is selected (a selection state), a video signal is input to the pixel 180102 from the signal line. A state (e.g., luminance, transmittance, or voltage of a storage capacitor) of the pixel 180102 is changed in accordance with the video signal input thereto.

When the pixel 180102 is not selected (a non-selection state), the video signal is not input to the pixel 180102. Note that the pixel 180102 holds a potential corresponding to the video signal which is input when selected; thus, the pixel 180102 maintains the state (e.g., luminance, transmittance, or voltage of a storage capacitor) in accordance with the video signal.

Note that a structure of the display device is not limited to that shown in FIG. 68. For example, an additional wiring (such as a scan line, a signal line, a power supply line, a capacitor line, or a common line) may be added in accordance with the structure of the pixel 180102. As another example, a circuit having various functions may be added.

FIG. 69 shows an example of a timing chart for describing an operation of a display device.

The timing chart of FIG. 69 shows one frame period corresponding to a period when an image of one screen is displayed. One frame period is not particularly limited, but is preferably 1/60 second or less so that a viewer does not perceive a flicker.

The timing chart of FIG. 69 shows timing of selecting the scan line G1 in the first row, the scan line Gi (one of the scan lines G1 to Gm) in the i-th row, the scan line Gi+1 in the (i+1)th row, and the scan line Gm in the m-th row.

At the same time as the scan line is selected, the pixel 180102 connected to the scan line is also selected. For example, when the scan line Gi in the i-th row is selected, the pixel 180102 connected to the scan line Gi in the i-th row is also selected.

The scan lines Gi to Gm are sequentially selected (hereinafter also referred to as scanned) from the scan line Gi in the first row to the scan line Gm in the m-th row. For example, while the scan line Gi in the i-th row is selected, the scan lines (Gi to Gi−1 and Gi+1 to Gm) other than the scan line Gi in the i-th row are not selected. Then, during the next period, the scan line Gi+1 in the (i+1)th row is selected. Note that a period during which one scan line is selected is referred to as one gate selection period.

Accordingly, when a scan line in a certain row is selected, video signals from the signal lines S1 to Sn are input to a plurality of pixels 180102 connected to the scan line, respectively. For example, while the scan line Gi in the i-th row is selected, given video signals are input from the signal lines S1 to Sn to the plurality of pixels 180102 connected to the scan line Gi in the i-th row, respectively. Thus, each of the plurality of pixels 180102 can be controlled individually by the scan signal and the video signal.

Next, the case where one gate selection period is divided into a plurality of subgate selection periods is described. FIG. 70 is a timing chart in the case where one gate selection period is divided into two subgate selection periods (a first subgate selection period and a second subgate selection period).

Note that one gate selection period may be divided into three or more subgate selection periods.

The timing chart of FIG. 70 shows one frame period corresponding to a period when an image of one screen is displayed. One frame period is not particularly limited, but is preferably 1/60 second or less so that a viewer does not perceive a flicker.

Note that one frame is divided into two subframes (a first subframe and a second subframe).

The timing chart of FIG. 70 shows timing of selecting the scan line Gi in the i-th row, the scan line Gi+1 in the (i+1)th row, the scan line Gj (one of the scan lines Gi+1 to Gm) in the j-th row, and the scan line Gj+1 (one of the scan lines Gi+1 to Gm) in the (j+1)th row.

At the same time as the scan line is selected, the pixel 180102 connected to the scan line is also selected. For example, when the scan line Gi in the i-th row is selected, the pixel 180102 connected to the scan line Gi in the i-th row is also selected.

The scan lines G1 to Gm are sequentially scanned in each subgate selection period. For example, in one gate selection period, the scan line Gi in the i-th row is selected in the first subgate selection period, and the scan line Gj in the j-th row is selected in the second subgate selection period. Thus, in one gate selection period, an operation can be performed as if the scan signals of two rows are selected. At this time, different video signals are input to the signal lines SI to Sn in the first subgate selection period and the second subgate selection period. Accordingly, different video signals can be input to a plurality of pixels 180102 connected to the i-th row and a plurality of pixels 180102 connected to the j-th row.

Next, a driving method for displaying images with high quality is described.

FIGS. 71A and 71B are views for describing high frequency driving.

FIG. 71A shows the case where one image and one intermediate image are displayed in one frame period 180400. Reference numerals 180401, 180402, 180403, and 180404 denote an image of one frame, an intermediate image of the frame, an image of the next frame, and an intermediate image of the next frame, respectively.

The intermediate image 180402 of the frame may be made based on image signals of the frame and the next frame. Alternatively, the intermediate image 180402 of the frame may be made from the image 180401 of the frame, or may be a black image. Accordingly, the quality of a moving image in a hold-type display device can be improved. Further, when one image and one intermediate image are displayed in one frame period 180400, there is an advantage in that consistency with a frame rate of the video signal can be easily obtained and an image processing circuit is not complicated.

FIG. 71B shows the case where one image and two intermediate images are displayed in a period with two successive one frame periods 180400 (two frame periods). Reference numeral 180411, 180412, 180413, and 180414 denote an image of the frame, an intermediate image of the frame, an intermediate image of the next frame, an image of a frame after next, respectively.

Each of the intermediate image 180412 of the frame and the intermediate image 180413 of the next frame may be made based on video signals of the frame, the next frame, and the frame after next. Alternatively, each of the intermediate image 180412 of the frame and the intermediate image 180413 of the next frame may be a black image. When one image and two intermediate images are displayed in two frame periods, there is an advantage in that operating frequency of a peripheral driver circuit is not so high and the quality of a moving image can be effectively improved.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 16

In this embodiment mode, a structure of an EL element is described. In particular, a structure of an organic EL element is described.

A structure of a mixed junction EL element is described. As an example, a structure is described, which includes a layer (a mixed layer) in which a plurality of materials among a hole injecting material, a hole transporting material, a light-emitting material, an electron transporting material, an electron injecting material, and the like are mixed (hereinafter referred to as a mixed junction type EL element), which is different from a stacked-layer structure where a hole injecting layer formed of a hole injecting material, a hole transporting layer formed of a hole transporting material, a light-emitting layer formed of a light-emitting material, an electron transporting layer formed of an electron transporting material, an electron injecting layer formed of an electron injecting material, and the like are clearly distinguished.

FIGS. 72A to 72E are schematic views each showing a structure of a mixed junction type EL element. Note that a layer interposed between an anode 190101 and a cathode 190102 corresponds to an EL layer.

FIG. 72A shows a structure in which an EL layer includes a hole transporting region 190103 formed of a hole transporting material and an electron transporting region 190104 formed of an electron transporting material. The hole transporting region 190103 is closer to the anode than the electron transporting region 190104. A mixed region 190105 including both the hole transporting material and the electron transporting material is provided between the hole transporting region 190103 and the electron transporting region 190104.

In a direction from the anode 190101 to the cathode 190102, a concentration of the hole transporting material in the mixed region 190105 is decreased and a concentration of the electron transporting material in the mixed region 190105 is increased.

Note that a concentration gradient can be freely set. For example, a ratio of concentrations of each functional material may be changed (a concentration gradient may be formed) in the mixed region 190105 including both the hole transporting material and the electron transporting material, without including the hole transporting region 190103 formed of only the hole transporting material. Alternatively, a ratio of concentrations of each functional material may be changed (a concentration gradient may be formed) in the mixed region 190105 including both the hole transporting material and the electron transporting material, without including the hole transporting region 190103 formed of only the hole transporting material and the electron transporting region 190104 formed of only the electron transporting material. Further alternatively, a ratio of concentrations may be changed depending on a distance from the anode or the cathode. Note that the ratio of concentrations may be changed continuously.

A region 190106 to which a light-emitting material is added is included in the mixed region 190105. A light emission color of the EL element can be controlled by the light-emitting material. Further, carriers can be trapped by the light-emitting material. As the light-emitting material, various fluorescent dyes as well as a metal complex having a quinoline skeleton, a benzoxazole skeleton, or a benzothiazole skeleton can be used. The light emission color of the EL element can be controlled by adding the light-emitting material.

As the anode 190101, an electrode material having a high work function is preferably used in order to inject holes efficiently. For example, a transparent electrode formed of indium tin oxide (ITO), indium zinc oxide (IZO), ZnO, SnO₂, In₂O₃, or the like can be used. When a light-transmitting property is not needed, the anode 190101 may be formed of an opaque metal material.

As the hole transporting material, an aromatic amine compound or the like can be used.

As the electron transporting material, a metal complex having a quinoline derivative, 8-quinolinol, or a derivative thereof as a ligand (especially tris(8-quinolinolato)aluminum (Alq₃)), or the like can be used.

As the cathode 190102, an electrode material having a low work function is preferably used in order to inject electrons efficiently. A metal such as aluminum, indium, magnesium, silver, calcium, barium, or lithium can be used by itself. Alternatively, an alloy of the aforementioned metal or an alloy of the aforementioned metal and another metal may be used.

FIG. 72B is the schematic view of the structure of the EL element, which is different from that of FIG. 72A. Note that the same portions as those in FIG. 72A are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 72B, a region to which a light-emitting material is added is not included. However, when a material (electron-transporting and light-emitting material) having both an electron transporting property and a light-emitting property, for example, tris(8-quinolinolato)aluminum (Alq₃) is used as a material added to the electron transporting region 190104, light emission can be performed.

Alternatively, as a material added to the hole transporting region 190103, a material (a hole-transporting and light-emitting material) having both a hole transporting property and a light-emitting property may be used.

FIG. 72C is the schematic view of the structure of the EL element, which is different from those of FIGS. 72A and 72B. Note that the same portions as those in FIGS. 72A and 72B are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 72C, a region 190107 included in the mixed region 190105 is provided, to which a hole blocking material having a larger energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital than the hole transporting material is added. The region 190107 to which the hole blocking material is added is provided closer to the cathode 190102 than the region 190106 in the mixed region 190105, to which the light-emitting material is added; thus, a recombination rate of carriers can be increased, and light emission efficiency can be increased. The structure provided with the region 190107 to which the hole blocking material is added is especially effective in an EL element which utilizes light emission (phosphorescence) by a triplet exciton.

FIG. 72D is the schematic view of the structure of the EL element, which is different from those of FIGS. 72A to 72C. Note that the same portions as those in FIGS. 72A to 72C are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 72D, a region 190108 included in the mixed region 190105 is provided, to which an electron blocking material having a larger energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital than the electron transporting material is added. The region 190108 to which the electron blocking material is added is provided closer to the anode 190101 than the region 190106 in the mixed region 190105, to which the light-emitting material is added; thus, a recombination rate of carriers can be increased, and light emission efficiency can be increased. The structure provided with the region 190108 to which the electron blocking material is added is especially effective in an EL element which utilizes light emission (phosphorescence) by a triplet exciton.

FIG. 72E is the schematic view of the structure of the mixed junction type EL element, which is different from those of FIGS. 72A to 72D. FIG. 72E shows an example of a structure where a region 190109 to which a metal material is added is included in part of an EL layer in contact with an electrode of the EL element. In FIG. 72E, the same portions as those in FIGS. 72A to 72D are denoted by the same reference numerals, and description thereof is omitted. In the structure shown in FIG. 72E, MgAg (an Mg—Ag alloy) may be used as the cathode 190102, and the region 190109 to which an Al (aluminum) alloy is added may be included in a region of the electron transporting region 190104 to which the electron transporting material is added, which is in contact with the cathode 190102, for example. With the aforementioned structure, oxidation of the cathode can be prevented, and electron injection efficiency from the cathode can be increased. Accordingly, the lifetime of the mixed junction type EL element can be extended. Further, driving voltage can be lowered.

As a method of forming the mixed junction type EL element, a co-evaporation method or the like can be used.

In the mixed junction type EL elements as shown in FIGS. 72A to 72E, a clear interface between the layers does not exist, and charge accumulation can be reduced. Accordingly, the lifetime of the EL element can be extended. Further, driving voltage can be lowered.

Note that the structures shown in FIGS. 72A to 72E can be implemented in free combination with each other.

In addition, a structure of the mixed junction type EL element is not limited to those described above. A known structure can be freely used.

An organic material which forms an EL layer of an EL element may be a low molecular material or a high molecular material. Alternatively, both of the materials may be used. When a low molecular material is used for an organic compound material, a film can be formed by an evaporation method. When a high molecular material is used for the EL layer, the high molecular material is dissolved in a solvent and a film can be formed by a spin coating method or an inkjet method.

The EL layer may be formed of a middle molecular material. In this specification, a middle molecule organic light-emitting material refers to an organic light-emitting material without a sublimation property and with a polymerization degree of approximately 20 or less. When a middle molecular material is used for the EL layer, a film can be formed by an inkjet method or the like.

Note that a low molecular material, a high molecular material, and a middle molecular material may be used in combination.

An EL element may utilize either light emission (fluorescence) by a singlet exciton or light emission (phosphorescence) by a triplet exciton.

Next, an evaporation device for manufacturing a display device applicable to the present invention is described with reference to drawings.

A display device applicable to the present invention may be manufactured to include an EL layer. The EL layer is formed including at least partially a material which exhibits electroluminescence. The EL layer may be formed of a plurality of layers having different functions. In this case, the EL layer may be formed of a combination of layers having different functions, which are also referred to as a hole injecting and transporting layer, a light-emitting layer, an electron injecting and transporting layer, and the like.

FIG. 73 shows a structure of an evaporation device for forming an EL layer over an element substrate provided with a transistor. In the evaporation device, a plurality of treatment chambers are connected to transfer chambers 190260 and 190261. Each treatment chamber includes a loading chamber 190262 for supplying a substrate, an unloading chamber 190263 for collecting the substrate, a heat treatment chamber 190268, a plasma treatment chamber 190272, deposition treatment chambers 190269 to 190271 and 190273 to 190275 for depositing an EL material, and a deposition treatment chamber 190276 for forming a conductive film which is formed of aluminum or contains aluminum as its main component as one electrode of an EL element. Gate valves 190277 a to 190277 m are provided between the transfer chambers and the treatment chambers, so that the pressure in each treatment chamber can be controlled independently, and cross contamination between the treatment chambers is prevented.

A substrate introduced into the transfer chamber 190260 from the loading chamber 190262 is transferred to a predetermined treatment chamber by an arm type transfer means 190266 capable of rotating. The substrate is transferred from a certain treatment chamber to another treatment chamber by the transfer means 190266. The transfer chambers 190260 and 190261 are connected by the deposition treatment chamber 190270 at which the substrate is transported by the transfer means 190266 and a transfer means 190267.

Each treatment chamber connected to the transfer chambers 190260 and 190261 is maintained in a reduced pressure state. Accordingly, in the evaporation device, deposition treatment of an EL layer is continuously performed without exposing the substrate to the room air. A display panel in which formation of the EL layer is finished is deteriorated due to moisture or the like in some cases. Accordingly, in the evaporation device, a sealing treatment chamber 190265 for performing sealing treatment before exposure to the room air in order to maintain the quality is connected to the transfer chamber 190261. Since the sealing treatment chamber 190265 is under atmospheric pressure or reduced pressure near atmospheric pressure, an intermediate treatment chamber 190264 is also provided between the transfer chamber 190261 and the sealing treatment chamber 190265. The intermediate treatment chamber 190264 is provided for transporting the substrate and buffering the pressure between the chambers.

An exhaust means is provided in the loading chamber, the unloading chamber, the transfer chamber, and the deposition treatment chamber in order to maintain reduced pressure in the chamber. As the exhaust means, various vacuum pumps such as a dry pump, a turbo-molecular pump, and a diffusion pump can be used.

In the evaporation device of FIG. 73, the number of treatment chambers connected to the transfer chambers 190260 and 190261 and structures thereof can be combined as appropriate in accordance with a stacked-layer structure of the EL element. An example of a combination is described below.

In the heat treatment chamber 190268, degasification treatment is performed by heating a substrate over which a lower electrode, an insulating partition wall, or the like is formed. In the plasma treatment chamber 190272, a surface of the lower electrode is treated with a rare gas or oxygen plasma. This plasma treatment is performed for cleaning the surface, stabilizing a surface state, or stabilizing a physical or chemical state (e.g., a work function) of the surface.

The deposition treatment chamber 190269 is for forming an electrode buffer layer which is in contact with one electrode of the EL element. The electrode buffer layer has a carrier injection property (hole injection or electron injection) and suppresses generation of a short-circuit or a black spot defect of the EL element. Typically, the electrode buffer layer is formed of an organic-inorganic hybrid material, has a resistivity of 5×10⁴ to 1×10⁶ Ωcm, and is formed having a thickness of 30 to 300 nm. Note that the deposition treatment chamber 190271 is for forming a hole transporting layer.

A light-emitting layer in an EL element has a different structure between the case of emitting single color light and the case of emitting white light. Deposition treatment chambers in the evaporation device are preferably arranged depending on the structure. For example, when three kinds of EL elements each having a different light emission color are formed in a display panel, it is necessary to form light-emitting layers corresponding to respective light emission colors. In this case, the deposition treatment chamber 190270 can be used for forming a first light-emitting layer, the deposition treatment chamber 190273 can be used for forming a second light-emitting layer, and the deposition treatment chamber 190274 can be used for forming a third light-emitting layer. By using different deposition treatment chambers for respective light-emitting layers, cross contamination due to different light-emitting materials can be prevented, and throughput of the deposition treatment can be improved.

Note that three kinds of EL elements each having a different light emission color may be sequentially deposited in each of the deposition treatment chambers 190270, 190273, and 190274. In this case, evaporation is performed by moving a shadow mask depending on a region to be deposited.

When an EL element which emits white light is formed, the EL element is formed by vertically stacking light-emitting layers of different light emission colors. In this case also, the element substrate can be sequentially transferred through the deposition treatment chambers so that each light-emitting layer is formed. Alternatively, different light-emitting layers can be formed continuously in the same deposition treatment chamber.

In the deposition treatment chamber 190276, an electrode is formed over the EL layer. The electrode can be formed by an electron beam evaporation method or a sputtering method, and preferably by a resistance heating evaporation method.

The element substrate in which formation of the electrode is finished is transferred to the sealing treatment chamber 190265 through the intermediate treatment chamber 190264. The sealing treatment chamber 190265 is filled with an inert gas such as helium, argon, neon, or nitrogen, and a sealing substrate is attached to a side of the element substrate where the EL layer is formed under the atmosphere so that the EL layer is sealed. In a sealed state, a space between the element substrate and the sealing substrate may be filled with an inert gas or a resin material. The sealing treatment chamber 190265 is provided with a dispenser which draws a sealing material, a mechanical element such as an arm or a fixing stage which fixes the sealing substrate to face the element substrate, a dispenser or a spin coater which fills the chamber with a resin material, or the like.

FIG. 74 shows an internal structure of a deposition treatment chamber. The deposition treatment chamber is maintained in a reduced pressure state. In FIG. 74, a space interposed between a top plate 190391 and a bottom plate 190392 corresponds to an internal space of the chamber, which is maintained in a reduced pressure state.

One or a plurality of evaporation sources are provided in the treatment chamber. This is because a plurality of evaporation sources are preferably provided when a plurality of layers having different compositions are formed or when different materials are co-evaporated. In FIG. 74, evaporation sources 190381 a, 190381 b, and 190381 c are attached to an evaporation source holder 190380. The evaporation source holder 190380 is held by a multi-joint arm 190383. The multi-joint arm 190383 allows the evaporation source holder 190380 to move within its movable range by stretching the joint. Alternatively, the evaporation source holder 190380 may be provided with a distance sensor 190382 to monitor a distance between the evaporation sources 190381 a to 190381 c and a substrate 190389 so that an optimal distance for evaporation is controlled. In this case, the multi-joint arm may be capable of moving toward upper and lower directions (Z direction) as well.

The substrate 190389 is fixed by using a substrate stage 190386 and a substrate chuck 190387 together. The substrate stage 190386 may have a structure where a heater is incorporated so that the substrate 190389 can be heated. The substrate 190389 is fixed to the substrate stage 190386 with the support of the substrate chuck 190387 and is transferred. At the time of evaporation, a shadow mask 190390 provided with an opening corresponding to an evaporation pattern can be used when needed. In this case, the shadow mask 190390 is arranged between the substrate 190389 and the evaporation sources 190381 a to 190381 c. The shadow mask 190390 adheres to the substrate 190389 or is fixed to the substrate 190389 with a certain interval therebetween by a mask chuck 190388. When alignment of the shadow mask 190390 is needed, the alignment is performed by arranging a camera in the treatment chamber and providing the mask chuck 190388 with a positioning means which slightly moves in X-Y-θ directions.

Each of the evaporation sources 190381 a to 190381 c is provided with an evaporation material supply means which continuously supplies an evaporation material to the evaporation source. The evaporation material supply means includes evaporation material supply sources 190385 a, 190385 b, and 190385 c, which are provided apart from the evaporation sources 190381 a, 190381 b, and 190381 c, and a material supply pipe 190384 which connects the evaporation source and the evaporation material supply source. Typically, the evaporation material supply sources 190385 a to 190385 c are provided corresponding to the evaporation sources 190381 a to 190381 c. In FIG. 74, the evaporation material supply source 190385 a corresponds to the evaporation source 190381 a, the evaporation material supply source 190385 b corresponds to the evaporation source 190381 b, and the evaporation material supply source 190385 c corresponds to the evaporation source 190381 c.

As a method for supplying an evaporation material, an airflow transfer method, an aerosol method, or the like can be employed. In an airflow transfer method, impalpable powder of an evaporation material is transferred in airflow to the evaporation sources 190381 a to 190381 c by using an inert gas or the like. In an aerosol method, evaporation is performed while material liquid in which an evaporation material is dissolved or dispersed in a solvent is transferred and aerosolized by an atomizer and the solvent in the aerosol is vaporized. In each case, the evaporation sources 190381 a to 190381 c are provided with a heating means, and a film is formed over the substrate 190389 by vaporizing the transferred evaporation material. In FIG. 74, the material supply pipe 190384 can be bent flexibly and is formed of a thin pipe which has enough rigidity not to be transformed even under reduced pressure.

When an airflow transfer method or an aerosol method is employed, film formation may be performed in the deposition treatment chamber under atmospheric pressure or lower, and preferably under a reduced pressure of 133 to 13300 Pa. The pressure can be adjusted while an inert gas such as helium, argon, neon, krypton, xenon, or nitrogen fills the deposition treatment chamber or is supplied (and exhausted at the same time) to the deposition treatment chamber. Note that an oxidizing atmosphere may be employed by introducing a gas such as oxygen or nitrous oxide in the deposition treatment chamber where an oxide film is formed. Alternately, a reducing atmosphere may be employed by introducing a gas such as hydrogen in the deposition treatment chamber where an organic material is deposited.

As another method for supplying an evaporation material, a screw may be provided in the material supply pipe 190384 to continuously push the evaporation material toward the evaporation source.

With this evaporation device, a film can be formed continuously with high uniformity even in the case of a large display panel. Since it is not necessary to supply an evaporation material to the evaporation source every time the evaporation material is run out, throughput can be improved.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 17

In this embodiment mode, examples of electronic devices according to the present invention are described.

FIG. 75 shows a display panel module combining a display panel 900101 and a circuit board 900111. The display panel 900101 includes a pixel portion 900102, a scan line driver circuit 900103, and a signal line driver circuit 900104. The circuit board 900111 is provided with a control circuit 900112, a signal dividing circuit 900113, and the like, for example. The display panel 900101 and the circuit board 900111 are connected by a connection wiring 900114. An FPC or the like can be used for the connection wiring.

In the display panel 900101, the pixel portion 900102 and part of peripheral driver circuits (a driver circuit having a low operation frequency among a plurality of driver circuits) may be formed over the same substrate by using transistors, and another part of the peripheral driver circuits (a driver circuit having a high operation frequency among the plurality of driver circuits) may be formed over an IC chip. Then, the IC chip may be mounted on the display panel 900101 by COG (Chip On Glass) or the like. Thus, the area of the circuit board 900111 can be reduced, and a small display device can be obtained. Alternatively, the IC chip may be mounted on the display panel 900101 by using TAB (Tape Automated Bonding) or a printed wiring board. Thus, the area of the display panel 900101 can be reduced, and a display device with a narrower frame can be obtained.

For example, in order to reduce power consumption, a pixel portion may be formed over a glass substrate by using transistors, and all peripheral circuits may be formed over an IC chip. Then, the IC chip may be mounted on a display device by COG or TAB.

A television receiver can be completed with the display panel module shown in FIG. 75. FIG. 76 is a block diagram showing a main structure of a television receiver. A tuner 900210 receives a video signal and an audio signal. The video signals are processed by an video signal amplifier circuit 900202; a video signal processing circuit 900203 which converts a signal output from the video signal amplifier circuit 900202 into a color signal corresponding to each color of red, green, and blue; and a control circuit 900212 which converts the video signal into an input specification of a driver circuit. The control circuit 900212 outputs signals to each of the scan line side and the signal line side. When digital driving is performed, a structure may be employed in which a signal dividing circuit 900213 is provided on the signal line side and an input digital signal is divided into m signals (m is a positive integer) to be supplied.

Among the signals received by the tuner 900210, an audio signal is transmitted to an audio signal amplifier circuit 900205, and an output thereof is supplied to a speaker 900207 through an audio signal processing circuit 900206. A control circuit 900208 receives control information on receiving station (receiving frequency) and volume from an input portion 900209 and transmits a signal to the tuner 900210 or the audio signal processing circuit 900206.

FIG. 77A shows a television receiver incorporated with a display panel module which is different from FIG. 76. In FIG. 77A, a display screen 900302 stored in a housing 900301 is formed using the display panel module. Note that speakers 900303, an operation switch 900304, and the like may be provided as appropriate.

FIG. 77B shows a television receiver in which only a display can be carried wirelessly. A battery and a signal receiver are incorporated in a housing 900312. The battery drives a display portion 900313 or a speaker portion 900317. The battery can be repeatedly charged by a charger 900310. The charger 900310 which is capable of transmitting and receiving a video signal can transmit the video signal to the signal receiver of the display. The housing 900312 is controlled by an operation key 900316. Alternatively, the device shown in FIG. 77B can transmit a signal to the charger 900310 from the housing 900312 by operating the operation key 900316. That is, the device may be an image and audio interactive communication device. Further alternatively, by operating the operation key 900316, a signal is transmitted to the charger 900310 from the housing 900312, and another electronic device is made to receive a signal which can be transmitted from the charger 900310; thus, the device can control communication of another electronic device. That is, the device may be a general-purpose remote control device. The present invention can be applied to the display portion 900313.

FIG. 78A shows a module combining a display panel 900401 and a printed wiring board 900402. The display panel 900401 may be provided with a pixel portion 900403 including a plurality of pixels, a first scan line driver circuit 900404, a second scan line driver circuit 900405, and a signal line driver circuit 900406 which supplies a video signal to a selected pixel.

The printed wiring board 900402 is provided with a controller 900407, a central processing unit (CPU) 900408, a memory 900409, a power supply circuit 9004010, an audio processing circuit 900411, a transmitting/receiving circuit 900412, and the like. The printed wiring board 900402 and the display panel 900401 are connected by a flexible printed circuit (FPC) 900413. The flexible printed circuit (FPC) 900413 may be provided with a capacitor, a buffer circuit, or the like so as to prevent noise on power supply voltage or a signal, and increase in rise time of a signal. Note that the controller 900407, the audio processing circuit 900411, the memory 900409, the central processing unit (CPU) 900408, the power supply circuit 900410, or the like can be mounted to the display panel 900401 by using a COG (Chip On Glass) method. By using a COG method, the size of the printed wiring board 900402 can be reduced.

Various control signals are input and output through an interface (I/F) portion 900414 provided for the printed wiring board 900402. An antenna port 900415 for transmitting and receiving a signal to/from an antenna is provided for the printed wiring board 900402.

FIG. 78B is a block diagram of the module shown in FIG. 78A. The module includes a VRAM 900416, a DRAM 900417, a flash memory 900418, and the like as the memory 900409. The VRAM 900416 stores data on an image displayed on a panel, the DRAM 900417 stores video data or audio data, and the flash memory 900418 stores various programs.

The power supply circuit 900410 supplies electric power for operating the display panel 900401, the controller 900407, the central processing unit (CPU) 900408, the audio processing circuit 900411, the memory 900409, and the transmitting/receiving circuit 900412. Note that the power supply circuit 900410 may be provided with a current source depending on a panel specification.

The central processing unit (CPU) 900408 includes a control signal generation circuit 900420, a decoder 900421, a register 900422, an arithmetic circuit 900423, a RAM 900424, an interface (I/F) portion 900419 for the central processing unit (CPU) 900408, and the like. Various signals input to the central processing unit (CPU) 900408 via the interface (I/F) portion 900414 are once stored in the register 900422, and subsequently input to the arithmetic circuit 900423, the decoder 900421, and the like. The arithmetic circuit 900423 performs operation based on the signal input thereto so as to designate a location to which various instructions are sent. On the other hand, the signal input to the decoder 900421 is decoded and input to the control signal generation circuit 900420. The control signal generation circuit 900420 generates a signal including various instructions based on the signal input thereto, and transmits the signal to the location designated by the arithmetic circuit 900423, specifically the memory 900409, the transmitting/receiving circuit 900412, the audio processing circuit 900411, and the controller 900407, for example.

The memory 900409, the transmitting/receiving circuit 900412, the audio processing circuit 900411, and the controller 900407 operate in accordance with respective instructions. Hereinafter, the operation is briefly described.

A signal input from an input means 900425 is transmitted via the interface (I/F) portion 900414 to the central processing unit (CPU) 900408 mounted to the printed wiring board 900402. The control signal generation circuit 900420 converts image data stored in the VRAM 900416 into a predetermined format depending on the signal transmitted from the input means 900425 such as a pointing device or a keyboard, and transmits the converted data to the controller 900407.

The controller 900407 performs data processing of the signal including the image data transmitted from the central processing unit (CPU) 900408 in accordance with the panel specification, and supplies the signal to the display panel 900401. The controller 900407 generates an Hsync signal, a Vsync signal, a clock signal CLK, alternating voltage (AC Cont), and a switching signal L/R based on power supply voltage input from the power supply circuit 900410 or various signals input from the central processing unit (CPU) 900408, and supplies the signals to the display panel 900401.

The transmitting/receiving circuit 900412 processes a signal which is to be transmitted and received as an electric wave by an antenna 900428. Specifically, the transmitting/receiving circuit 900412 may include a high-frequency circuit such as an isolator, a band pass filter, a VCO (voltage controlled oscillator), an LPF (low pass filter), a coupler, or a balun, A signal including audio information among signals transmitted and received by the transmitting/receiving circuit 900412 is transmitted to the audio processing circuit 900411 in accordance with an instruction from the central processing unit (CPU) 900408.

The signal including the audio information which is transmitted in accordance with the instruction from the central processing unit (CPU) 900408 is demodulated into an audio signal by the audio processing circuit 900411 and transmitted to a speaker 900427. An audio signal transmitted from a microphone 900426 is modulated by the audio processing circuit 900411 and transmitted to the transmitting/receiving circuit 900412 in accordance with an instruction from the central processing unit (CPU) 900408.

The controller 900407, the central processing unit (CPU) 900408, the power supply circuit 900410, the audio processing circuit 900411, and the memory 900409 can be mounted as a package of this embodiment mode.

It is needless to say that this embodiment mode is not limited to a television receiver and can be applied to various uses, such as a monitor of a personal computer, and especially as a large display medium such as an information display board at the train station, the airport, or the like, or an advertisement display board on the street.

Next, a structure example of a mobile phone according to the present invention is described with reference to FIG. 79.

A display panel 900501 is detachably incorporated in a housing 900530. The shape or the size of the housing 900530 can be changed as appropriate in accordance with the size of the display panel 900501. The housing 900530 which fixes the display panel 900501 is fitted in a printed wiring board 900531 to be assembled as a module.

The display panel 900501 is connected to the printed wiring board 900531 through an FPC 900513. The printed wiring board 900531 is provided with a speaker 900532, a microphone 900533, a transmitting/receiving circuit 900534, and a signal processing circuit 900535 including a CPU, a controller, and the like. Such a module, an input means 900536, and a battery 900537 are combined and stored in a housing 900539. A pixel portion of the display panel 900501 is provided to be seen from an opening window formed in the housing 900539.

In the display panel 900501, the pixel portion and part of peripheral driver circuits (a driver circuit having a low operation frequency among a plurality of driver circuits) may be formed over the same substrate by using transistors, and another part of the peripheral driver circuits (a driver circuit having a high operation frequency among the plurality of driver circuits) may be formed over an IC chip. Then, the IC chip may be mounted on the display panel 900501 by COG (Chip On Glass). Alternatively, the IC chip may be connected to a glass substrate by using TAB (Tape Automated Bonding) or a printed wiring board. With such a structure, power consumption of a display device can be reduced, and operation time of the mobile phone per charge can be extended. Further, reduction in cost of the mobile phone can be realized.

The mobile phone shown in FIG. 79 has various functions such as, but not limited to, a function of displaying various kinds of information (e.g., a still image, a moving image, and a text image); a function of displaying a calendar, a date, the time, and the like on a display portion; a function of operating or editing the information displaying on the display portion; a function of controlling processing by various kinds of software (programs); a function of wireless communication; a function of communicating with another mobile phone, a fixed phone, or an audio communication device by using the wireless communication function; a function of connecting with various computer networks by using the wireless communication function; a function of transmitting or receiving various kinds of data by using the wireless communication function; a function of operating a vibrator in accordance with incoming call, reception of data, or an alarm; and a function of generating a sound in accordance with incoming call, reception of data, or an alarm.

In a mobile phone shown in FIG. 80, a main body (A) 900601 provided with operation switches 900604, a microphone 900605, and the like is connected to a main body (B) 900602 provided with a display panel (A) 900608, a display panel (B) 900609, a speaker 900606, and the like by using a hinge 900610 so that the mobile phone can be opened and closed. The display panel (A) 900608 and the display panel (B) 900609 are placed in a housing 900603 of the main body (B) 900602 together with a circuit board 900607. Each of pixel portions of the display panel (A) 900608 and the display panel (B) 900609 is arranged to be seen from an opening window formed in the housing 900603.

Specifications of the display panel (A) 900608 and the display panel (B) 900609, such as the number of pixels, can be set as appropriate in accordance with functions of a mobile phone 900600. For example, the display panel (A) 900608 can be used as a main screen and the display panel (B) 900609 can be used as a sub-screen.

A mobile phone according to this embodiment mode can be changed in various modes depending on functions or applications thereof. For example, it may be a camera-equipped mobile phone by incorporating an imaging element in a portion of the hinge 900610. When the operation switches 900604, the display panel (A) 900608, and the display panel (B) 900609 are placed in one housing, the aforementioned effects can be obtained. Further, a similar effect can be obtained when the structure of this embodiment mode is applied to an information display terminal equipped with a plurality of display portions.

The mobile phone in FIG. 80 has various functions such as, but not limited to, a function of displaying various kinds of information (e.g., a still image, a moving image, and a text image); a function of displaying a calendar, a date, the time, and the like on a display portion; a function of operating or editing the information displaying on the display portion; a function of controlling processing by various kinds of software (programs); a function of wireless communication; a function of communicating with another mobile phone, a fixed phone, or an audio communication device by using the wireless communication function; a function of connecting with various computer networks by using the wireless communication function; a function of transmitting or receiving various kinds of data by using the wireless communication function; a function of operating a vibrator in accordance with incoming call, reception of data, or an alarm; and a function of generating a sound in accordance with incoming call, reception of data, or an alarm.

The present invention can be applied to various electronic devices. Specifically, the present invention can be applied to a display portion of an electronic device. Examples of such electronic devices include cameras such as a video camera and a digital camera, a goggle-type display, a navigation system, an audio reproducing device (such as car audio components and audio components), a computer, a game machine, a portable information terminal (such as a mobile computer, a mobile phone, a mobile game machine, and an electronic book), and an image reproducing device provided with a recording medium (specifically, a device which reproduces a recording medium such as a digital versatile disc (DVD) and has a display for displaying the reproduced image).

FIG. 81A shows a display, which includes a housing 900711, a support base 900712, a display portion 900713, and the like. The display shown in FIG. 81A can have various functions such as, but not limited to, a function of displaying various kinds of information (e.g., a still image, a moving image, and a text image) on the display portion.

FIG. 81B shows a camera, which includes a main body 900721, a display portion 900722, an image receiving portion 900723, operation keys 900724, an external connection port 900725, a shutter button 900726, and the like. The camera shown in FIG. 81B can have various functions such as, but not limited to, a function of photographing a still image and a moving image; a function of automatically adjusting the photographed image (the still image or the moving image); a function of storing the photographed image in a recording medium (provided externally or incorporated in the camera); and a function of displaying the photographed image on the display portion.

FIG. 81C shows a computer, which includes a main body 900731, a housing 900732, a display portion 900733, a keyboard 900734, an external connection port 900735, a pointing device 900736, and the like. The computer shown in FIG. 81C can have various functions such as, but not limited to, a function of displaying various kinds of information (e.g., a still image, a moving image, and a text image) on the display portion; a function of controlling processing by various kinds of software (programs); a communication function such as wireless communication or wire communication; a function of connecting with various computer networks by using the communication function; and a function of transmitting or receiving various kinds of data by using the communication function.

FIG. 81D shows a mobile computer, which includes a main body 900741, a display portion 900742, a switch 900743, operation keys 900744, an infrared port 900745, and the like. The mobile computer shown in FIG. 81D can have various functions such as, but not limited to, a function of displaying various kinds of information (e.g., a still image, a moving image, and a text image) on the display portion; a touch panel function provided on the display portion; a function of displaying a calendar, a date, the time, and the like on the display portion; a function of controlling processing by various kinds of software (programs); a function of wireless communication; a function of connecting with various computer networks by using the wireless communication function; and a function of transmitting or receiving various kinds of data by using the wireless communication function.

FIG. 81E shows a portable image reproducing device provided with a recording medium (e.g., a DVD reproducing device), which includes a main body 900751, a housing 900752, a display portion A 900753, a display portion B 900754, a recording medium (e.g., DVD) reading portion 900755, operation keys 900756, a speaker portion 900757, and the like. The display portion A 900753 can mainly display image information, and the display portion B 900754 can mainly display text information.

FIG. 81F shows a goggle-type display, which includes a main body 900761, a display portion 900762, an earphone 900763, a support portion 900764, and the like. The goggle-type display shown in FIG. 81F can have various functions such as, but not limited to, a function of displaying an image (e.g., a still image, a moving image, and a text image) which is externally obtained on the display portion.

FIG. 81G shows a portable game machine, which includes a housing 900771, a display portion 900772, speaker portions 900773, operation keys 900774, a recording medium insert portion 900775, and the like. The portable game machine shown in FIG. 81G can have various functions such as, but not limited to, a function of reading a program or data stored in the recording medium to display on the display portion; and a function of sharing information by wireless communication with another portable game machine.

FIG. 81H shows a digital camera having a television reception function, which includes a housing 900781, a display portion 900782, operation keys 900783, a speaker 900784, a shutter button 900785, an image receiving portion 900786, an antenna 900787, and the like. The digital camera having the television reception function shown in FIG. 81H can have various functions such as, but not limited to, a function of photographing a still image and a moving image; a function of automatically adjusting the photographed image; a function of obtaining various kinds of information from the antenna; a function of storing the photographed image or the information obtained from the antenna; and a function of displaying the photographed image or the information obtained from the antenna on the display portion.

As shown in FIGS. 81A to 81H, the electronic device according to the present invention includes a display portion for displaying some kind of information. In the electronic device according to the present invention, when pieces of data overlap with each other, the overlapping data is stored in a memory; thus, frequency of circuit operations can be decreased. Accordingly, the electronic device has low power consumption and can drive with a battery for a long time.

Next, application examples of the display device according to the present invention are described.

FIG. 82 shows an example in which the display device according to the present invention is incorporated in a constructed object. FIG. 82 shows a housing 900810, a display portion 900811, a remote control device 900812 which is an operation portion, a speaker portion 900813, and the like. The display device according to the present invention is incorporated in the constructed object as a wall-mounted display device, which can be provided without requiring a large space.

FIG. 83 shows another example in which the display device according to the present invention is incorporated in a constructed object. A display panel 900901 is incorporated with a prefabricated bath 900902, and a person who takes a bath can view the display panel 900901. The display panel 900901 has a function of displaying information by an operation by the person who takes a bath; and a function of being used as an advertisement or an entertainment means.

Note that the display device according to the present invention can be provided not only to a side wall of the prefabricated bath 900902 as shown in FIG. 83, but also to various places. For example, the display device can be incorporated with part of a mirror, a bathtub itself, or the like. At this time, the shape of the display panel 900901 may be changed in accordance with the shape of the mirror or the bathtub.

FIG. 84 shows another example in which the display device according to the present invention is incorporated in a constructed object. A display panel 901002 is bent and attached to a curved surface of a column-shaped object 901001. Note that here, a utility pole is described as the column-shaped object 901001.

The display panel 901002 shown in FIG. 84 is provided at a position higher than a human viewpoint. When the display panels 901002 are provided in constructed objects which stand together in large numbers outdoors, such as utility poles, advertisement can be performed to an unspecified number of viewers. Since it is easy for the display panels 901002 to display the same images and instantly switch images by external control, highly efficient information display and advertisement effect can be obtained. By provision of self-luminous display elements, the display panel 901002 can be useful as a highly visible display medium even at night. When the display panel 901002 is provided in the utility pole, a power supply means for the display panel 901002 can be easily obtained. In an emergency such as disaster, the display panel 901002 can also be used as a means to transmit correct information to victims rapidly.

Note that an example of the display panel 901002 includes a display panel in which a switching element such as an organic transistor is provided over a film-shaped substrate and a display element is driven so that an image is displayed.

Note that in this embodiment mode, a wall, a column-shaped object, and a prefabricated bath are shown as examples of constructed objects; however, this embodiment mode is not limited thereto, and various constructed objects can be provided with the display device according to the present invention.

Next, examples where the display device according to the present invention is incorporated with a moving object are described.

FIG. 85 shows an example in which the display device according to the present invention is incorporated with a car. A display panel 901101 is incorporated with a car body 901102 and can display an operation of the car body or information input from inside or outside the car body on demand. Note that a navigation function may be provided.

The display device according to the present invention can be provided not only to the car body 901102 as shown in FIG. 85, but also to various places. For example, the display device can be incorporated with a glass window, a door, a steering wheel, a gear shift, a seat, a rear-view mirror, and the like. At this time, the shape of the display panel 901101 may be changed in accordance with the shape of an object provided with the display device.

FIGS. 86A and 86B show examples where the display device according to the present invention is incorporated with a train car.

FIG. 86A shows an example in which a display panel 901202 is provided in glass of a door 901201 in a train car, which has an advantage compared with a conventional advertisement using paper in that labor cost for changing an advertisement is not necessary. Since the display panel 901202 can instantly switch images displaying on a display portion by an external signal, images on the display panel can be switched in every time period when types of passengers on the train are changed, for example. Thus, a more effective advertisement effect can be obtained.

FIG. 86B shows an example in which the display panels 901202 are provided to a glass window 901203 and a ceiling 901204 as well as the glass of the door 901201 in the train car. In such a manner, the display device according to the present invention can be easily provided to a place where a display device has been difficult to be provided conventionally; thus, an effective advertisement effect can be obtained. Further, the display device according to the present invention can instantly switch images displayed on a display portion by an external signal; thus, cost and time for changing an advertisement can be reduced, and more flexible advertisement management and information transmission can be realized.

Note that the display device according to the present invention can be provided not only to the door 901201, the glass window 901203, and the ceiling 901204 as shown in FIGS. 86A and 86B, but also to various places. For example, the display device can be incorporated with a strap, a seat, a handrail, a floor, and the like. At this time, the shape of the display panel 901202 may be changed in accordance with the shape of an object provided with the display device.

FIGS. 87A and 87B show an example in which the display device according to the present invention is incorporated with a passenger airplane.

FIG. 87A shows the shape of a display panel 901302 provided on a ceiling 901301 above a seat of the passenger airplane when the display panel 901302 is used. The display panel 901302 is incorporated with the ceiling 901301 with a hinge portion 901303, and a passenger can view the display panel 901302 by stretching of the hinge portion 901303. The display panel 901302 has a function of displaying information by an operation by the passenger and a function of being used for an advertisement or an entertainment means. As shown in FIG. 87B, when the hinge portion is bent so that the display panel is stored in the ceiling 901301, safety in taking-off and landing can be assured. Note that in an emergency, the display panel can also be used for an information transmission means and a guide light by lighting a display element in the display panel.

Note that the display device according to the present invention can be provided not only to the ceiling 901301 as shown in FIGS. 87A and 87B, but also to various places. For example, the display device can be incorporated with a seat, a table attached to a seat, an armrest, a window, and the like. A large display panel which a plurality of people can view may be provided on a wall of an airframe. At this time, the shape of the display panel 901302 may be changed in accordance with the shape of an object provided with the display device.

Note that in this embodiment mode, bodies of a train car, a car, and an airplane are shown as moving objects; however, the present invention is not limited thereto, and the display device according to the present invention can be provided to various objects such as a motorcycle, an four-wheel drive car (including a car, a bus, and the like), a train (including a monorail, a railroad car, and the like), and a vessel. Since the display device according to the present invention can instantly switch images displayed on a display panel in a moving object by an external signal, the moving object provided with the display device according to the present invention can be used as an advertisement display board for an unspecified number of customers, an information display board in disaster, and the like.

Note that although this embodiment mode is described with reference to various drawings, the contents (or part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in another drawing. Further, much more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or part of the contents) described in each drawing in this embodiment mode can be freely applied to, combined with, or replaced with the contents (or part of the contents) described in a drawing in another embodiment mode or embodiment. Further, much more drawings can be formed by combining each part in each drawing in this embodiment mode with part of another embodiment mode or embodiment.

Note that this embodiment mode shows examples of embodying, slightly transforming, partially modifying, improving, describing in detail, or applying the contents (or part of the contents) described in other embodiment modes and embodiments, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment mode.

Embodiment 1

In this embodiment, a more specific example of the signal line driver circuit included in the display device shown in FIG. 1 is described.

FIG. 14 shows an example of a circuit diagram of the signal line driver circuit. The signal line driver circuit shown in FIG. 14 includes a shift register 501, a sampling circuit 502, a first latch 503, a second latch 504, a third latch 505, a level shifter 506, and a buffer 507. Note that although a signal line driver circuit including three latches of the first latch 503, the second latch 504, and the third latch 505 as memory circuits is described as an example in this embodiment, the number of memory circuits is not limited to this.

The shift register 501 includes a plurality of delay flip flops (DFFs) 508. The shift register 501 generates a timing signal, a pulse of which is sequentially shifted, in accordance with the start pulse signal S—SP and the clock signal S-CLK which are input, and the timing signal is input to the sampling circuit 502 in the next stage.

The sampling circuit 502 includes a plurality of memory elements (LATs) 509. The sampling circuit 502 sequentially samples video signals in accordance with the pulse of the input timing signal, and data of the sampled video signals is written to the memory elements 509.

The first latch 503 includes a plurality of memory elements (LATs) 510. The second latch 504 includes a plurality of memory elements (LATs) 511. The third latch 505 includes a plurality of memory elements (LATs) 512. The number of each of the memory elements 510, the memory elements 511, and the memory elements 512 is preferably the same as or more than the number of pixels of one line in a pixel portion.

The writing latch signal WS₁ and the reading latch signal RS₁ are input to the first latch 503. The writing latch signal WS₂ and the reading latch signal RS₂ are input to the second latch 504. The writing latch signal WS₃ and the reading latch signal RS₃ are input to the third latch 505.

The data which is written to the memory element 509 in the sampling circuit 502 is written to and held in the memory elements 510 included in the first latch 503, the memory elements 511 included in the second latch 504, or the memory elements 512 included in the third latch 505. Writing of the data to the memory elements 510 is controlled by the writing latch signal WS₁; writing of the data to the memory elements 511 is controlled by the writing latch signal WS₂; and writing of the data to the memory elements 512 is controlled by the writing latch signal WS₃.

The data held in the memory elements 510, the memory elements 511, or the memory elements 512 is input to the level shifter 506 in the next stage as a video signal. Input of the video signal to the level shifter 506 is controlled by the reading latch signals RS₁ to RS₃.

The level shifter 506 controls voltage amplitude of the input video signal and inputs the input video signal to the buffer 507 in the next stage. The buffer 507 shapes a waveform of the input video signal and input the video signal to the pixel portion.

Although this embodiment is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 2

In this embodiment, a more specific example of the signal line driver circuit included in the display device shown in FIG. 12 is described.

FIG. 15 shows an example of a circuit diagram of the signal line driver circuit. The signal line driver circuit shown in FIG. 15 includes a shift register 601, a sampling circuit 602, a first latch 603, a second latch 604, a third latch 605, and a D/A converter circuit 606. Note that a signal line driver circuit including three latches of the first latch 603, the second latch 604, and the third latch 605 as memory circuits is described as an example in this embodiment, the number of memory circuits is not limited to this.

The shift register 601 includes a plurality of delay flip flops (DFFs) 608. The shift register 601 generates a timing signal, a pulse of which is sequentially shifted, in accordance with a start pulse signal S—SP and a clock signal S-CLK which are input, and the timing signal is input to the sampling circuit 602 in the next stage.

The sampling circuit 602 includes a plurality of memory elements (LATs) 609. The number of the memory elements 609 is preferably the same as or more than the number obtained by multiplying the number of pixels of one line in a pixel portion by the number of bits of a video signal. Note that although an example in which the number of bits of the video signal is three is described in FIG. 15, the number of bits of the video signal is not limited to this. The sampling circuit 602 sequentially samples video signals in accordance with the pulse of the input timing signal, and data of the sampled video signals is written to the memory elements 609.

The first latch 603 includes a plurality of memory elements (LATs) 610. The second latch 604 includes a plurality of memory elements (LATs) 611. The third latch 605 includes a plurality of memory elements (LATs) 612. The number of each of the memory elements 610, the memory elements 611, and the memory elements 612 is preferably the same as or more than the number obtained by multiplying the number of pixels of one line in the pixel portion by the number of bits of the video signal.

The writing latch signal WS₁ and the reading latch signal RS₁ are input to the first latch 603. The writing latch signal WS₂ and the reading latch signal RS₂ are input to the second latch 604. The writing latch signal WS₃ and the reading latch signal RS₃ are input to the third latch 605.

The data which is written to the memory element 609 in the sampling circuit 602 is written to and is held in the memory elements 610 included in the first latch 603, the memory elements 611 included in the second latch 604, or the memory elements 612 included in the third latch 605. Writing of the data to the memory elements 610 is controlled by the writing latch signal WS₁; writing of the data to the memory elements 611 is controlled by the writing latch signal WS₂; and writing of the data to the memory elements 612 is controlled by the writing latch signal WS₃.

Then, the data held in the memory elements 610, the memory elements 611, or the memory elements 612 is input to the D/A converter circuit 606 in the next stage as a video signal. Input of the video signal to the D/A converter circuit 606 is controlled by the reading latch signals RS₁ to RS₃. The D/A converter circuit 606 converts the input video signal into an analog video signal and inputs it to the pixel portion in the next stage.

Although this embodiment is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 3

In this embodiment, a structure of a memory element in a memory circuit included in a display device of the present invention is described.

FIG. 20 shows an example of a circuit diagram of the memory element. FIG. 20 shows structures of memory elements 801 to 803 included in three memory circuits, respectively. The memory element 802 is connected to the next stage of the memory element 801. The memory element 803 is connected to the next stage of the memory element 802. Note that although the number of memory elements included in each memory circuit is one in FIG. 20, the number of memory elements included in each memory circuit is actually the same as or more than the number of pixels of one line. In the case where a digital video signal is converted into an analog video signal in a signal line driver circuit, the number of memory elements included in each circuit is the same as or more than the number obtained by multiplying the number of pixels of one line by the number of bits of the video signal.

The writing latch signal WS₁ and the reading latch signal RS₁ are input to the memory element 801. The writing latch signal WS₂ and the reading latch signal RS₂ are input to the memory element 802. The writing latch signal WS₃ and a reading latch signal RS₃ are input to the memory elements 803.

Since the memory elements 801 to 803 have the same circuit structure in FIG. 20, the structure of each memory element is described in more detail by giving the memory element 801 as an example.

The memory element 801 includes a clocked inverter 804, a clocked inverter 806, an inverter 805, and a switching circuit 807. Operations of the clocked inverter 804 and the clocked inverter 806 are controlled by the writing latch signal WS₁ input to the clocked inverter 804 and the clocked inverter 806. A sampled video signal is input from a sampling circuit to the clocked inverter 804. Output of the clocked inverter 804 is supplied to the inverter 805. The inverter 805 and the clocked inverter 806 form a flip-flop circuit by supplying output of the inverter 805 to input of the clocked inverter 806 and supplying output of the clocked inverter 806 to input of the inverter 805. In addition, the output of the inverter 805 is supplied to the next stage of the memory circuit, e.g., a signal line of a pixel portion or a D/A converter circuit through the switching circuit 807.

An operation of the switching circuit 807 is controlled by the reading latch signal RS₁ input to the switching circuit 807. FIG. 20 shows an example in which the switching circuit 807 includes a transmission gate 808 and an inverter 809. The reading latch signal RS₁ and a signal obtained by inverting the reading latch signal RS₁ by the inverter 809 are input to the transmission gate 808, and switching of the transmission gate 808 is controlled by these signals.

The contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 4

In this embodiment, a structure of a pixel portion included in an active matrix light-emitting device which is a kind of a display device of the present invention is described.

An active matrix light-emitting device includes a light-emitting element which corresponds to a display element in each pixel. Since a light-emitting element emits light by itself, the light-emitting element has high visibility, dose not need a backlight which is necessary for a liquid crystal display device, is suitable for reduction in thickness, and does not have limitations on the viewing angle. Although a light-emitting device using an organic light-emitting element (OLED) which is a kind of a light-emitting element is described in this embodiment, the present invention may be a light-emitting device using another light-emitting element.

An OLED includes a layer including a material in which luminescence (electroluminescence) generated by application of an electric field can be obtained, an anode layer, and a cathode layer. As electroluminescence, there are luminescence (fluorescence) at the time of returning to a ground state from a singlet-excited state and luminescence (phosphorescence) at the time of returning to a ground state from a triplet-excited state. A light-emitting device of the present invention may use either one of fluorescence and phosphorescence or both fluorescence and phosphorescence.

FIG. 16A is an enlarged view of a pixel portion 301 of a light-emitting device of this embodiment. The pixel portion 301 includes a plurality of pixels 304 arranged in matrix. Reference signs S1 to Sx denote signals lines; reference signs VI to Vx denote power supply lines; and reference signs G1 to Gy denote scan lines. In this embodiment, the pixel 304 includes one of the signal lines SI to Sx, one of the power supply lines V1 to Vx, and one of the scan lines Gi to Gy.

FIG. 16B is an enlarged view of the pixel 304. In FIG. 16B, a reference numeral 305 denotes a switching transistor. A gate electrode of the switching transistor 305 is connected to a scan line Gj (j=One of 1 to y). One of a source region and a drain region of the switching transistor 305 is connected to a signal line Si (i=one of 1 to x). The other of the source region and the drain region of the switching transistor 305 is connected to a gate electrode of a driving transistor 306. In addition, a storage capacitor 308 included in each pixel is provided between a power supply line Vi (i=one of 1 to x) and the gate electrode of the driving transistor 306.

The storage capacitor 308 is provided to hold gate voltage (a potential difference between the gate electrode and a source region) of the driving transistor 306 when the switching transistor 305 is off. Note that although the structure in which the storage capacitor 308 is provided is described in this embodiment, the present invention is not limited to this structure and the storage capacitor 308 is not necessarily provided.

One of the source region and a drain region of the driving transistor 306 is connected to the power supply line Vi (i=one of 1 to x). The other of the source region and the drain region of the driving transistor 306 is connected to a light-emitting element 307. The light-emitting element 307 includes an anode, a cathode, and an electroluminescent layer provided between the anode and the cathode. When the anode is connected to the source region or the drain region of the driving transistor 306, the anode corresponds to a pixel electrode and the cathode corresponds to a counter electrode. Alternatively, when the cathode is connected to the source region or the drain region of the driving transistor 306, the cathode corresponds to the pixel electrode and the anode corresponds to the counter electrode.

Predetermined voltage is applied to each of the counter electrode of the light-emitting element 307 and the power supply line Vi.

The scan line Gj is selected in accordance with pulses of selection signals input to the scan lines G1 to Gy from a scan line driver circuit. That is, when the pixel 304 of a line corresponding to the scan line Gj is selected, the switching transistor 305, the gate electrode of which is connected to the scan line Gj, in the pixel 304 of the line is turned on. Then, when a video signal is input to the signal line Si, the gate voltage of the driving transistor 306 is determined in accordance with voltage of the video signal. When the driving transistor 306 is turned on, the power supply line Vi and the light-emitting element 307 are electrically connected, so that the light-emitting element 307 emits light by supply of current. Alternatively, when the driving transistor 306 is turned off, the power supply line Vi and the light-emitting element 307 are not electrically connected, so that supply of current to the light-emitting element 307 is not performed and the light-emitting element 307 does not emit light.

Note that the switching transistor 305 and the driving transistor 306 can be either n-channel transistors or p-channel transistors. Note that when the source region or the drain region of the driving transistor 306 is connected to the anode of the light-emitting element 307, the driving transistor 306 is preferably a p-channel transistor. Alternatively, when the source region or the drain region of the driving transistor 306 is connected to the cathode of the light-emitting element 307, the driving transistor 306 is preferably an n-channel transistor.

Each of the switching transistor 305 and the driving transistor 306 may have a multi-gate structure such as a double-gate structure or a triple-gate structure instead of a single-gate structure.

Note that the present invention can be applied to not only a display device including pixels having the circuit structure shown in FIGS. 16A and 16B but also a display device including pixels having various circuit structures. The pixel included in the display device of the present invention may have a threshold voltage compensation circuit structure in which the threshold voltage of the driving transistor can be compensated, a current input circuit structure in which the threshold voltage and mobility of the driving transistor can be compensated by input of current, or the like, for example.

The contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 5

In this embodiment, a structure of a pixel portion included in an active matrix liquid crystal display device which is a kind of a display device of the present invention is described.

FIG. 17 is an enlarged view of a pixel portion 401 of a liquid crystal display device of the present invention. In FIG. 17, the pixel portion 401 includes a plurality of pixels 402 arranged in matrix. Reference signs S1 to Sx denote signals lines, and reference signs G1 to Gy denote scan lines. In this embodiment, the pixel 402 includes one of the signal lines SI to Sx and one of the scan lines G1 to Gy.

The pixel 402 includes a transistor 403 functioning as a switching element, a liquid crystal cell 404 corresponding to a display element, and a storage capacitor 405. The liquid crystal cell 404 includes a pixel electrode, a counter electrode, and liquid crystals held between the pixel electrode and the counter electrode. A gate electrode of the transistor 403 is connected to a scan line Gj (j=one of 1 to x). One of a source region and a drain region of the transistor 403 is connected to a signal line Si (i=one of 1 to x). The other of the source region and the drain region of the transistor 403 is connected to the pixel electrode of the liquid crystal cell 404. In addition, one of two electrodes of the storage capacitor 405 is connected to the pixel electrode of the liquid crystal cell 404. The other of the two electrodes of the storage capacitor 405 is connected to a common electrode. The common electrode may be connected to either the counter electrode of the liquid crystal cell 404 or another scan line.

The scan line Gj is selected in accordance with pulses of selection signals input to the scan lines Gi to Gy from a scan line driver circuit. That is, when the pixel 402 of a line corresponding to the scan line Gj is selected, the transistor 403, the gate electrode of which is connected to the scan line Gj, in the pixel 402 of the line is turned on. Then, when a video signal is input to the signal line Si from a signal line driver circuit, voltage is applied between the pixel electrode and the counter electrode of the liquid crystal cell in accordance with the video signal. Transmissivity of the liquid crystal cell 404 is determined in accordance with a level of the voltage applied between the pixel electrode and the counter electrode. In addition, the voltage between the pixel electrode and the counter electrode of the liquid crystal cell 404 is held in the storage capacitor 405.

The contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 6

In this embodiment, timing during which video signals are input to a pixel portion in one frame period is described with reference to FIGS. 13A and 13B.

FIG. 13A is a timing chart showing timing during which videos signal are input to a pixel portion when one frame period is divided into subframe periods SF1 to SF6. The horizontal axis represents time and the vertical axis represents a scanning direction of a line selected by a scan line driver circuit. FIG. 13A shows an example in which a 6-bit video signal is used and one frame period is divided into six (the same number as the number of bits) subframe periods. Note that the number of bits of the video signal is not limited to six in the present invention.

Each of the subframe periods SF1 to SF6 includes a writing period Ta for inputting a video signal to each pixel. In the writing period Ta, pixels of respective lines are sequentially selected by the scan line driver circuit. Then, a video signal is input to the pixels of the selected line from a signal line driver circuit. Then, display is performed in accordance with the video signal sequentially from the pixels of the line in which input of the video signal is completed. When input of the video signals to the pixels of all the lines is completed, the writing period is completed. Note that since a video signal for one bit is input to the pixel portion in one writing period, completion of all the writing periods Ta corresponds to completion of input of the 6-bit video signal.

Then, when one writing period is completed, display is continuously performed in accordance with video signal input to the pixel portion until writing period of the next subframe period appears. Next, a writing period corresponding to another subframe period appears, and the above-described operation is repeated. Then, when all the subframe periods sequentially appear, one frame period is formed.

When all the subframe periods in one frame period appear, an image having gray scale levels can be displayed. The number of gray scales can be determined by controlling luminance of a display element in each subframe period. For example, when 64 gray scale levels are displayed by a 6-bit video signal, the ratio of the length of the subframe periods SF1 to SF6 is 2⁵:2⁴:2³:2²:2¹: 2⁰ sequentially from the longest when the number of gray scale levels is changed linearly.

Note that although luminance of the display element included in the pixel is controlled in accordance with the video signal in the above-described operation, the present invention is not limited to this structure. For example, a non-display period during which luminance of the display element is forcibly made the lowest regardless of a video signal may be provided. Note that the non-display period is not necessarily provided. However, when the length of the subframe period is shorter than the length of the writing period, it is necessary to provide a non-display period as described above. When a non-display period is provided, there is no need for concurrently inputting video signals to pixels of two or more rows in the pixel portion.

Note that operations may be performed by further dividing one subframe period into a plurality of subframe periods. In this case, each of the divided subframe periods includes the writing period Ta.

Next, the case is described in which only one writing period Ta appears in one frame period. FIG. 13B is a timing chart showing timing during which video signals are input to a pixel portion. The horizontal axis represents time and the vertical axis represents a scanning direction of a line selected by a scan line driver circuit.

In FIG. 13B, pixels of respective lines are sequentially selected by the scan line driver circuit in the writing period Ta. Then, an analog video signal is input to the pixels of the selected line from a signal line driver circuit. Then, in the writing period Ta, display is performed in accordance with the video signal sequentially from the pixels of the line in which input of the video signal is completed. When input of the video signals to the pixels of all the lines is completed, the writing period is completed. Next, display is performed in accordance with the video signal input to the pixel portion in the writing period Ta until the next frame period appears.

Note that the length of the writing period Ta in FIG. 13B can be set as appropriate by a designer as long as it is within one frame period. When the length of the writing period Ta is approximately the same as one frame period, driving frequency of the signal line driver circuit at the time of writing the video signal can be reduced and power consumption can also be reduced.

The contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 7

In this embodiment mode, a light-emitting device which is a kind of a display device of the present invention is given as an example, and an appearance thereof is described with reference to FIGS. 18A and 18B. FIG. 18A is a top plan view of a panel in which a transistor and a light-emitting element formed over a first substrate are sealed between the first substrate and a second substrate by a sealant. FIG. 18B corresponds to a cross-sectional view taken along a line A-A′ in FIG. 18A.

A sealant 4020 is provide so as to surround a pixel portion 4002, a signal line driver circuit 4003, and a scan line driver circuit 4004 which are provided over a first substrate 4001. A second substrate 4006 is provided over the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004. Thus, the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 are sealed between the first substrate 4001 and the second substrate 4006 together with a filler 4007 by the sealant 4020.

Each of the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 which are provided over the first substrate 4001 includes a plurality of transistors. FIG. 18B illustrates a transistor 4008 included in the signal line driver circuit 4003, and a driving transistor 4009 and a switching transistor 4010 which are included in the pixel portion 4002.

A light-emitting element 4011 uses part of a wiring 4017 connected to a source region or a drain region of the driving transistor 4009 as a pixel electrode. In addition, the light-emitting element 4011 includes a counter electrode 4012 and an electroluminescent layer 4013 as well as the pixel electrode. Note that the structure of the light-emitting element 4011 is not limited to the structure shown in this embodiment. The structure of the light-emitting element 4011 can be changed as appropriate in accordance with a direction of light extracted from the light-emitting element 4011, polarity of the driving transistor 4009, or the like.

Although various signals and voltages supplied to the pixel portion 4002, the signal line driver circuit 4003, or the scan line driver circuit 4004 are not shown in the cross-sectional view in FIG. 18B, various signals and voltages are supplied from a connection terminal 4016 through extraction wirings 4014 and 4015.

In this embodiment, the connection terminal 4016 is formed using the same conductive film as the counter electrode 4012 included in the light-emitting element 4011. The extraction wiring 4014 is formed using the same conductive film as the wiring 4017. The extraction wiring 4015 is formed using the same conductive film as gate electrodes included in the driving transistor 4009, the switching transistor 4010, and the transistor 4008, respectively.

The connection terminal 4016 is electrically connected to a terminal included in an FPC 4018 through an anisotropic conductive film 4019.

Glass, metal (typically, stainless steel), ceramic, or plastic can be used for the first substrate 4001 and the second substrate 4006. Note that the second substrate 4006 located in the direction of light extracted from the light-emitting element 4011 necessarily has light-transmitting properties. Thus, a light-transmitting material such as a glass plate, a plastic plate, a polyester film, or an acryl film is preferably used for the second substrate 4006.

In addition, an ultraviolet curable resin or a thermoset resin can be used for the filler 4007 as well as inert gas such as nitrogen or argon. In this embodiment, an example in which nitrogen is used for the filler 4007 is described.

Although this embodiment is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

Embodiment 8

Since power consumption of a display device of the present invention can be suppressed, the display device of the present invention is suitable for a display portion included in a handheld portable electronic device such as a mobile phone, a portable game machine, an electronic book, a video camera, or a digital still camera.

As an electronic device which can use the display device of the present invention, a goggle display (a head mounted display), a navigation system, an audio reproducing device (e.g., a car audio or an audio component set), a laptop computer, an image reproducing device provided with a recording medium (typically, a device for reproducing a recording medium such as a digital versatile disc (DVD) and having a display for displaying the reproduced image), and the like can be given. FIGS. 19A to 19C show specific examples of these electronic devices.

FIG. 19A shows a mobile phone, which includes a main body 2101, a display portion 2102, an audio input portion 2103, an audio output portion 2104, and operation keys 2105. By using the display device of the present invention for the display portion 2102, a mobile phone in which power consumption can be suppressed can be obtained.

FIG. 19B shows a video camera, which includes a main body 2601, a display portion 2602, a housing 2603, an external connection port 2604, a remote control receiving portion 2605, an image receiving portion 2606, a battery 2607, an audio input portion 2608, operation keys 2609, an eyepiece portion 2610, and the like. By using the display device of the present invention for the display portion 2602, a video camera in which power consumption can be suppressed can be obtained.

FIG. 19C shows an image display device, which includes a housing 2401, a display portion 2402, a speaker portion 2403, and the like. By using the display device of the present invention for the display portion 2402, an image display device in which power consumption can be suppressed can be obtained. Note that the image display device corresponds to all image display devices for displaying images, such as those for personal computers, television broadcast reception, and advertisement display.

As described above, the application range of the present invention is extremely wide and the present invention can be applied to electronic devices in all fields.

Although this embodiment is described with reference to various drawings, the contents (or may be part of the contents) described in each drawing can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in another drawing. Further, even more drawings can be formed by combining each part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described in each drawing of this embodiment can be freely applied to, combined with, or replaced with the contents (or may be part of the contents) described in a drawing in another embodiment mode or embodiment. Further, even more drawings can be formed by combining each part with part of another embodiment mode or embodiment in the drawings of this embodiment.

This embodiment shows an example of an embodied case of the contents (or may be part of the contents) described in other embodiment modes and embodiments, an example of slight transformation thereof, an example of partial modification thereof, an example of improvement thereof, an example of detailed description thereof, an application example thereof, an example of related part thereof, or the like. Therefore, the contents described in other embodiment modes and embodiments can be freely applied to, combined with, or replaced with this embodiment.

This application is based on Japanese Patent Application serial No. 2007-004106 filed with Japan Patent Office on Jan. 12, 2007, the entire contents of which are hereby incorporated by reference. 

1. A display device comprising: a pixel portion including a plurality of pixels; and a signal line driver circuit, wherein the signal line driver circuit includes a first memory circuit which can hold pieces of data of the video signals corresponding to a plurality of line periods which appear discontinuously.
 2. A display device according to claim 1, further comprising a scan line driver circuit selecting the plurality of pixels in each line.
 3. A display device according to claim 1, further comprising a sampling circuit for sampling video signals, wherein the memory circuit stores the sampled video signals and inputs the sampled video signals to the plurality of pixels.
 4. A display device according to claim 1, wherein the first memory circuit is a latch circuit.
 5. A display device according to claim 1, wherein the signal line driver circuit further includes a D/A converter circuit converting the video signals output from the plurality of memory circuits into analog video signals.
 6. A display device according to claim 1, further comprising: at least one second memory circuit for storing the pieces of data of the video signals corresponding to the plurality of line periods; and a data comparison circuit configured to read the pieces of data of the video signals from the at least one second memory circuits, compare the pieces of the data, and extract a group including a plurality of line periods among which pieces of data of video signals correspond to each other.
 7. A display device according to claim 6, wherein the data comparison circuit is configured to control the first memory circuit so that writing of the video signals corresponding to each other is performed only once during the plurality of line periods.
 8. A display device comprising: at least one first memory circuit configured to store pieces of data of video signals corresponding to a plurality of line periods; a data comparison circuit configured to read the pieces of data of the video signals from the at least one first memory circuit, compare the pieces of data, and extract a plurality of groups each including a plurality of line periods in which pieces of data of video signals correspond to each other; a pixel portion including a plurality of pixels; and a signal line driver circuit including a plurality of second memory circuits.
 9. A display device according to claim 8, wherein the plurality of second memory circuits are latch circuits.
 10. A display device according to claim 8, wherein the data comparison portion includes: a counter configured to count a number of the plurality of line periods included in each of the plurality of groups; and an arithmetic circuit selecting at least one of the plurality of groups in accordance with the number of the plurality of line periods.
 11. A display device according to claim 10, wherein the data comparison circuit is configured to control the plurality of memory circuits so that writing of the video signals is performed only once during the plurality of line periods included in each of the selected at least one group among the plurality of groups. 